x86/efi: move common keyring handler functions to new file

x86/efi: move common keyring handler functions to new file

BugLink: https://bugs.launchpad.net/bugs/1866909
The handlers to add the keys to the .platform keyring and blacklisted
hashes to the .blacklist keyring is common for both the uefi and powerpc
mechanisms of loading the keys/hashes from the firmware.

This patch moves the common code from load_uefi.c to keyring_handler.c

Signed-off-by: Nayna Jain <nayna@linux.ibm.com>
Acked-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Eric Richter <erichte@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/1573441836-3632-4-git-send-email-nayna@linux.ibm.com
(cherry picked from commit ad723674d6758478829ee766e3f1a2a24d56236f)
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>