libpayload: Clean up CFLAGS

- Add -ffreestanding and -fomit-frame-pointer for all
  platforms.
- Add ARMv7 specific flags to the armv7 Makefile

Change-Id: I71ab1b096e505940cc20c266bccd43917bcfad3a
Signed-off-by: Stefan Reinauer <reinauer@google.com>
Reviewed-on: https://gerrit.chromium.org/gerrit/56104
Commit-Queue: Stefan Reinauer <reinauer@chromium.org>
Reviewed-by: Stefan Reinauer <reinauer@chromium.org>
Tested-by: Stefan Reinauer <reinauer@chromium.org>
Reviewed-on: http://review.coreboot.org/4317
Tested-by: build bot (Jenkins)
Reviewed-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>

payloads/libpayload/arch/armv7/Makefile.inc

@@ -27,6 +27,8 @@
 ## SUCH DAMAGE.
 ##
 
+CFLAGS += -ffixed-r8 -mfloat-abi=hard -marm -mabi=aapcs-linux
+
 head.o-y += head.S
 libc-y += main.c sysinfo.c
 libc-y += timer.c coreboot.c util.S