verifiers: Framework core

Verifiers framework provides core file verification functionality which
can be used by various security mechanisms, e.g., UEFI secure boot, TPM,
PGP signature verification, etc.

The patch contains PGP code changes and probably they should be extracted
to separate patch for the sake of clarity.

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

grub-core/Makefile.core.def

@@ -894,6 +894,11 @@ module = {
   cppflags = '-I$(srcdir)/lib/posix_wrap';
 };
 
+module = {
+  name = verifiers;
+  common = commands/verifiers.c;
+};
+
 module = {
   name = hdparm;
   common = commands/hdparm.c;