MAINTAINERS: add Ilias Apalodimas to EFI PAYLOAD as co-maintainer

Ilias has since long been reviewing UEFI patches.
Now he has volunteered to assist me in maintaining the sub-system.

Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Acked-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>