ARM: disable KCOV for trusted foundations code

The ARM trusted foundations code is currently broken in linux-next when
CONFIG_KCOV_INSTRUMENT_ALL is set:

  /tmp/ccHdQsCI.s: Assembler messages:
  /tmp/ccHdQsCI.s:37: Error: .err encountered
  /tmp/ccHdQsCI.s:38: Error: .err encountered
  /tmp/ccHdQsCI.s:39: Error: .err encountered
  scripts/Makefile.build:311: recipe for target 'arch/arm/firmware/trusted_foundations.o' failed

I could not find a function attribute that lets me disable
-fsanitize-coverage=trace-pc for just one function, so this turns it off
for the entire file instead.

Link: http://lkml.kernel.org/r/20180529103636.1535457-1-arnd@arndb.de
Fixes: 75851720 ("arm: port KCOV to arm")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Olof Johansson <olof@lixom.net>
Tested-by: Olof Johansson <olof@lixom.net>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/arm/firmware/Makefile

 obj-$(CONFIG_TRUSTED_FOUNDATIONS)	+= trusted_foundations.o
+
+# tf_generic_smc() fails to build with -fsanitize-coverage=trace-pc
+KCOV_INSTRUMENT                := n