x86: efi: app: Fix broken EFI application

The EFI application does not boot currently. It's due to the call
to syscon_get_by_driver_data() in cpu_init_r() maps to nowhere as
CONFIG_SYSCON is not included in the configuration.

EFI application is built as a shared library, so GCC won't complain
during the build process if some symbols are not found. GCC will
simply put these symbols into the .plt section and expect dynamic
loader to fix these up.

While we are here, remove some commands and drivers that are not
needed at present.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>