commonlib/bsd/helpers: Remove redundancy with libpayload defines

Move STRINGIFY() from coreboot string.h to commonlib/bsd/helpers.h
Remove redundant defines from libpayload.h and libpayloads' standard
headers.

Signed-off-by: Jakub Czapiga <jacz@semihalf.com>
Change-Id: I3263b2aa7657759207bf6ffda750d839e741f99c
Reviewed-on: https://review.coreboot.org/c/coreboot/+/62921
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>

src/commonlib/bsd/include/commonlib/bsd/helpers.h

@@ -126,4 +126,10 @@
 #define retry(attempts, condition, ...) \
 	_retry_impl(attempts, condition, __VA_ARGS__)
 
+/* Stringify a token */
+#ifndef STRINGIFY
+#define _STRINGIFY(x)	#x
+#define STRINGIFY(x)	_STRINGIFY(x)
+#endif
+
 #endif /* COMMONLIB_BSD_HELPERS_H */