eficonfig: add UEFI Secure Boot Key enrollment interface

This commit adds the menu-driven UEFI Secure Boot Key
enrollment interface. User can enroll PK, KEK, db
and dbx by selecting file.
Only the signed EFI Signature List(s) with an authenticated
header, typically '.auth' file, is accepted.

To clear the PK, KEK, db and dbx, user needs to enroll the null key
signed by PK or KEK.

Signed-off-by: Masahisa Kojima <masahisa.kojima@linaro.org>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>