verifiers: Rename verify module to pgp module

Just for clarity. No functional change.

Signed-off-by: Daniel Kiper <daniel.kiper@oracle.com>
Reviewed-by: Ross Philipson <ross.philipson@oracle.com>

grub-core/Makefile.core.def

@@ -888,8 +888,8 @@ module = {
 };
 
 module = {
-  name = verify;
+  name = pgp;
-  common = commands/verify.c;
+  common = commands/pgp.c;
   cflags = '$(CFLAGS_POSIX)';
   cppflags = '-I$(srcdir)/lib/posix_wrap';
 };