efi: hii: add keyboard layout package support

Allow for handling keyboard layout package in HII database protocol.

A package can be added or deleted in HII database protocol, but
we don't set 'current' keyboard layout as there is no driver that
requests a keyboard layout.

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Signed-off-by: Alexander Graf <agraf@suse.de>