util/crossgcc: Update GMP from 6.2.1 to 6.3.0

Change-Id: I67d443cb15d89482b20b01f4068502b16ac8fc8e
Signed-off-by: Elyes Haouas <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/76865
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin L Roth <gaumless@gmail.com>

Documentation/releases/coreboot-4.22-relnotes.md

@@ -21,7 +21,7 @@ Update this document with changes that should be in the release notes.
 
 ### Toolchain updates
 
-* To be filled in immediately before the release by the release team
+* Upgrade GMP from 6.2.1 to 6.3.0
 
 ### Additional coreboot changes