Attached patch moves functions out of the huge libpayload.h into headers

Attached patch moves functions out of the huge libpayload.h into headers
according to libc/posix traditions, to simplify porting applications to
payloads.

It also adds a couple of functions:
strcasecmp, strncasecmp, strcat, strtol, strspn, strcspn, strtok_r,
strtok, perror, exit, getpagesize

Signed-off-by: Patrick Georgi <patrick.georgi@coresystems.de>
Acked-by: Stefan Reinauer <stepan@coresystems.de>
git-svn-id: svn://svn.coreboot.org/coreboot/trunk@5643 2b7e53f0-3cfb-0310-b3e9-8179ed1497e1