ARM: Tell the linker memset and memcpy are functions.

The memset and memcpy functions are assembled as ARM code, likely because
that's the default of the assembler. Without special annotation, the assembler
and linker don't know that those symbols are functions which need special
handling so that ARM/thumb issues are handled properly. This change adds that
annotation which gets those functions working in Coreboot which is compiled as
thumb. Libpayload and depthcharge are compiled as ARM so they don't *need* the
annotation since it just works out in ARM mode, but it's the safe thing to do
in case we change that in the future.

We should explicitly select ARM vs. thumb when assembling assembly files to be
consistent across builds and toolchains.

BUG=None
TEST=Built with the assembly versions of memcpy and memset turned on and saw
that we could boot after this change where we couldn't before. Disassembled a
function which calls memset and saw that it was using the blx instruction
which can change mode instead of the bl instruction which can't.
BRANCH=None

Change-Id: Ic3ef4faf17d3467b5042c944106b8743d517cce3
Signed-off-by: Gabe Black <gabeblack@google.com>
Reviewed-on: https://gerrit.chromium.org/gerrit/58728
Commit-Queue: Gabe Black <gabeblack@chromium.org>
Reviewed-by: Gabe Black <gabeblack@chromium.org>
Tested-by: Gabe Black <gabeblack@chromium.org>
Reviewed-by: David Hendricks <dhendrix@chromium.org>
Reviewed-by: Stefan Reinauer <reinauer@google.com>

payloads/libpayload/arch/armv7/memcpy.S

@@ -57,6 +57,7 @@
 
 /* Prototype: void *memcpy(void *dest, const void *src, size_t n); */
 
+.type memcpy, function
 .globl memcpy
 memcpy:
 

payloads/libpayload/arch/armv7/memset.S

@@ -27,6 +27,7 @@
  * memset again.
  */
 
+.type memset, function
 .globl memset
 memset:
 	ands	r3, r0, #3		@ 1 unaligned?

src/arch/armv7/memcpy.S

@@ -57,6 +57,7 @@
 
 /* Prototype: void *memcpy(void *dest, const void *src, size_t n); */
 
+.type memcpy, function
 .globl memcpy
 memcpy:
 

src/arch/armv7/memset.S

@@ -27,6 +27,7 @@
  * memset again.
  */
 
+.type memset, function
 .globl memset
 memset:
 	ands	r3, r0, #3		@ 1 unaligned?