efi_loader: implement InstallProtocolInterface

efi_install_protocol_interface up to now only returned an error code.

The patch implements the UEFI specification for InstallProtocolInterface
with the exception that it will not create new handles.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Alexander Graf <agraf@suse.de>