The .data.rel.ro.local section has the same semantics as .data.rel.ro
here, so include it in the .rodata section of the decompressor.
Additionally since the .printk_index section isn't usable outside of
the core kernel, discard it in the decompressor. Avoids these warnings:

arm-linux-gnueabi-ld: warning: orphan section `.data.rel.ro.local' from `arch/arm/boot/compressed/fdt_rw.o' being placed in section `.data.rel.ro.local'
arm-linux-gnueabi-ld: warning: orphan section `.printk_index' from `arch/arm/boot/compressed/fdt_rw.o' being placed in section `.printk_index'
Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/linux-mm/202209080545.qMIVj7YM-lkp@intel.com
Cc: Russell King <linux@armlinux.org.uk>
Cc: linux-arm-kernel@lists.infradead.org
Signed-off-by: Kees Cook <keescook@chromium.org>