security/vboot: Limit vboot verification code access to only verstage

security/vboot: Limit vboot verification code access to only verstage

Make vboot verification code accessible in only verstage.
Vboot verification code in vboot_logic.c is being used
in verstage. Due to support function vboot_save_data(),
so core functionality in vboot_logic.c is made available in romstage.
The patch decouples the support function frm vboot_logic.c to
limit itself to verstage.

BUG=b:155544643
TEST=Verified on hatch

Signed-off-by: Sridhar Siricilla <sridhar.siricilla@intel.com>
Change-Id: Id1ede45c4dffe90afcef210eabaa657cf92a9335
Reviewed-on: https://review.coreboot.org/c/coreboot/+/40562
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: Rizwan Qureshi <rizwan.qureshi@intel.com>