efi: Move x86 over to use the common efi_main() function

Fill in the required helper functions and call efi_main_common() to
do everything else.

Delete the old efi_main() function.

Signed-off-by: Simon Glass <sjg@chromium.org>

include/efi_stub.h

@@ -120,6 +120,9 @@ efi_status_t arch_efi_main_init(struct efi_priv *priv,
  */
 void arch_efi_jump_to_payload(struct efi_priv *priv);
 
+efi_status_t EFIAPI efi_main_common(efi_handle_t image,
+				    struct efi_system_table *sys_table);
+
 /* true if we must use the hardware UART directory (EFI not available) */
 extern bool use_hw_uart;