libpayload: Deduplicate strtol and strtoull

Our strtol() and strtoull() function contain almost exactly the same
code. This is a) bad in general and b) may cause the code to get out of
sync, such as it recently happened with CB:32029.

This patch changes strtol() to be based on strtoull() so that the main
parsing code exists only once, and also adds a strtoll() to round off
the library. Also fix the bounds imposed by strtoul() to be based on the
actual length of a 'long', not hardcoded to 32-bits (which is not
equivalent on all architectures).

Change-Id: I919c65a773cecdb11739c3f22dd0d182ed50c07f
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/32086
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

payloads/libpayload/include/stdlib.h

@@ -186,6 +186,7 @@ static inline void *xmemalign_work(size_t align, size_t size, const char *file,
  * @{
  */
 long int strtol(const char *s, char **nptr, int base);
+long long int strtoll(const char *s, char **nptr, int base);
 unsigned long int strtoul(const char *s, char **nptr, int base);
 unsigned long long int strtoull(const char *s, char **nptr, int base);
 long atol(const char *nptr);