MAINTAINERS: add UEFI commands to EFI PAYLOAD

Add the following files to EFI PAYLOAD:

- cmd/bootefi.c
- cmd/efidebug.c
- cmd/eficonfig.c
- cmd/nvedit_efi.c

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>