MIPS: Fix vmlinuz build for 32bit-only math shells

POSIX requires $((<expression>)) arithmetic in sh only to have long
arithmetic so on 32-bit sh binaries might do only 32-bit arithmetic but
the arithmetic done in arch/mips/boot/compressed/Makefile needs 64-bit.

I play with the AR7 platform, so VMLINUX_LOAD_ADDRESS is
0xffffffff94100000, and for an example 4MiB kernel
VMLINUZ_LOAD_ADDRESS is made out to be:
----
alex@berk:~$ bash -c 'printf "%x\n" $((0xffffffff94100000 + 0x400000))'
ffffffff94500000
alex@berk:~$ dash -c 'printf "%x\n" $((0xffffffff94100000 + 0x400000))'
80000000003fffff
----

The former is obviously correct whilst the later breaks things royally.

Fortunately working with only the lower 32bit's works for both bash and
dash:
----
$ bash -c 'printf "%x\n" $((0x94100000 + 0x400000))'
94500000
$ dash -c 'printf "%x\n" $((0x94100000 + 0x400000))'
94500000
----

So, we can split the original 64bit string to two parts, and only
calculate the low 32bit part, which is big enough (1GiB kernel sizes
anyone?) for a normal Linux kernel image file, now, we calculate the
VMLINUZ_LOAD_ADDRESS like this:

1. if present, append top 32bit of VMLINUX_LOAD_ADDRESS" as a prefix
2. get the sum of the low 32bit of VMLINUX_LOAD_ADDRESS + VMLINUX_SIZE

This patch fixes vmlinuz kernel builds on systems where only a
32bit-only math shell is available.

Patch Changelog:
  Version 2
    - simplified method by using 'expr' for 'substr' and making it work
	with dash once again
  Version 1
    - Revert the removals of '-n "$(VMLINUX_SIZE)"' to avoid the error
        of "make clean"
    - Consider more cases of the VMLINUX_LOAD_ADDRESS
  Version 0
    - initial release
Signed-off-by: Alexander Clouter <alex@digriz.org.uk>
Acked-by: Wu Zhangjin <wuzhangjin@gmail.com>
Patchwork: http://patchwork.linux-mips.org/patch/861/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/boot/compressed/Makefile

@@ -14,8 +14,11 @@
 
 # compressed kernel load addr: VMLINUZ_LOAD_ADDRESS > VMLINUX_LOAD_ADDRESS + VMLINUX_SIZE
 VMLINUX_SIZE := $(shell wc -c $(objtree)/$(KBUILD_IMAGE) 2>/dev/null | cut -d' ' -f1)
-VMLINUX_SIZE := $(shell [ -n "$(VMLINUX_SIZE)" ] && echo $$(($(VMLINUX_SIZE) + (65536 - $(VMLINUX_SIZE) % 65536))))
-VMLINUZ_LOAD_ADDRESS := 0x$(shell [ -n "$(VMLINUX_SIZE)" ] && printf %x $$(($(VMLINUX_LOAD_ADDRESS) + $(VMLINUX_SIZE))))
+VMLINUX_SIZE := $(shell [ -n "$(VMLINUX_SIZE)" ] && echo -n $$(($(VMLINUX_SIZE) + (65536 - $(VMLINUX_SIZE) % 65536))))
+# VMLINUZ_LOAD_ADDRESS = concat "high32 of VMLINUX_LOAD_ADDRESS" and "(low32 of VMLINUX_LOAD_ADDRESS) + VMLINUX_SIZE"
+HIGH32 := $(shell A=$(VMLINUX_LOAD_ADDRESS); [ $${\#A} -gt 10 ] && expr substr "$(VMLINUX_LOAD_ADDRESS)" 3 $$(($${\#A} - 10)))
+LOW32 := $(shell [ -n "$(HIGH32)" ] && A=11 || A=3; expr substr "$(VMLINUX_LOAD_ADDRESS)" $${A} 8)
+VMLINUZ_LOAD_ADDRESS := 0x$(shell [ -n "$(VMLINUX_SIZE)" -a -n "$(LOW32)" ] && printf "$(HIGH32)%08x" $$(($(VMLINUX_SIZE) + 0x$(LOW32))))
 
 # set the default size of the mallocing area for decompressing
 BOOT_HEAP_SIZE := 0x400000