[efi] Default to using raw x86 I/O

The EFI_CPU_IO_PROTOCOL is not available on all EFI platforms.  In
particular, it is not available under OVMF, as used for qemu.

Since the EFI_CPU_IO_PROTOCOL is an abomination of unnecessary
complexity, banish it and use raw I/O instead.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/config/defaults/efi.h

  */
 
 #define UACCESS_EFI
-#define IOAPI_EFI
+#define IOAPI_X86
 #define PCIAPI_EFI
 #define CONSOLE_EFI
 #define TIMER_EFI