configs: stm32mp1: enable uefi related commands

The board can boot with UEFI. With the latest changes in U-Boot's
EFI subsystem we also have support for EFI runtime variables, without
SetVariable support.  We can also store the EFI variables in a file on the
ESP partition and preserve them across reboots.
The env and efidebug commands are missing in order to configure
EFI variables and the efibootmgr though.  Since U-Boot's default config
enables other EFI related commands (e.g bootefi), let's add the env related
and efidebug commands and allow users to do that

Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>