efi: Set RUN_64BIT correctly for the EFI app

The U-Boot EFI app can run as a 64-bit program, so set the Kconfig
correctly in that case. Make sure it doesn't build SPL, since there is
no need to switch from 32 to 64 bit when running.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/efi-x86_app64_defconfig b/configs/efi-x86_app64_defconfig
index dae4884..f1cf43c 100644
--- a/configs/efi-x86_app64_defconfig
+++ b/configs/efi-x86_app64_defconfig
@@ -4,6 +4,7 @@
 CONFIG_DEFAULT_DEVICE_TREE="efi-x86_app"
 CONFIG_DEBUG_UART_BASE=0
 CONFIG_DEBUG_UART_CLOCK=0
+CONFIG_X86_RUN_64BIT=y
 CONFIG_VENDOR_EFI=y
 CONFIG_TARGET_EFI_APP64=y
 CONFIG_DEBUG_UART=y