libpayload: Don't sneak in compiler includes

The way we got to include the compiler includes was kind of whacky.
Instead of mixing in potentially problematic headers, make libpayload
self-contained by adding some missing header files. Also clean up
conflicting definitions of size_t throughout the tree.

Signed-off-by: Stefan Reinauer <reinauer@google.com>

Change-Id: I0ad1194de1a00b7133c5477c00eb167d63a2ee85
Reviewed-on: https://gerrit.chromium.org/gerrit/47608
Reviewed-by: Ronald G. Minnich <rminnich@chromium.org>
Commit-Queue: Stefan Reinauer <reinauer@google.com>
Tested-by: Stefan Reinauer <reinauer@google.com>
Reviewed-on: http://review.coreboot.org/3058
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

payloads/libpayload/include/armv7/arch/types.h

@@ -53,9 +53,6 @@ typedef signed long long s64;
 typedef long time_t;
 typedef long suseconds_t;
 
-typedef unsigned long size_t;
-typedef long ssize_t;
-
 #ifndef NULL
 #define NULL ((void *)0)
 #endif