efi: Use struct efi_gop_mode_info in struct efi_entry_gopmode

efi: Use struct efi_gop_mode_info in struct efi_entry_gopmode

Since C99 flexible array members are allowed at the end of structures.
We require C11.

Use struct efi_gop_mode_info in the definition of struct efi_entry_gopmode
to avoid code duplication and unnecessary conversions.

Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>