efi: Switch x86 and ARM to use the unified stub

Now that the stub code is unified, switch over to it, dropping the
individual efi_main() functions.

Series-to: concept
Cover-letter:
efi: Unify the scripts and start-up code
We have two scripts which run QEMU, one for EFI and one for bare metal.
They have similar options so it seems reasonable to try to unify them a
bit. This series creates a common file and adjusts arguments so they are
consistent across both scripts.

The EFI app for ARM and x86 have different start-up code but in fact
the code is quiet similar. This series creates a new common main
program, called efi_main_common() which is used for both architectures.
The small number of differences are handled in arch-specific code.
END

include/efi_stub.h

@@ -120,9 +120,6 @@ 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;