[efi] Add "reboot" command for EFI

Abstract out the ability to reboot the system to a separate reboot()
function (with platform-specific implementations), add an EFI
implementation, and make the existing "reboot" command available under
EFI.

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

src/config/defaults/efi.h

@@ -19,8 +19,11 @@
 #define BOFM_EFI
 #define ENTROPY_NULL
 #define TIME_NULL
+#define REBOOT_EFI
 
 #define	IMAGE_EFI		/* EFI image support */
 #define	IMAGE_SCRIPT		/* iPXE script image support */
 
+#define	REBOOT_CMD		/* Reboot command */
+
 #endif /* CONFIG_DEFAULTS_EFI_H */

src/config/defaults/linux.h

@@ -16,6 +16,7 @@
 #define SANBOOT_NULL
 #define ENTROPY_LINUX
 #define TIME_LINUX
+#define REBOOT_NULL
 
 #define DRIVERS_LINUX
 

src/config/defaults/pcbios.h

@@ -20,6 +20,7 @@ FILE_LICENCE ( GPL2_OR_LATER );
 #define SANBOOT_PCBIOS
 #define ENTROPY_RTC
 #define TIME_RTC
+#define REBOOT_PCBIOS
 
 #define	IMAGE_ELF		/* ELF image support */
 #define	IMAGE_MULTIBOOT		/* MultiBoot image support */

src/config/reboot.h

@@ -0,0 +1,16 @@
+#ifndef CONFIG_REBOOT_H
+#define CONFIG_REBOOT_H
+
+/** @file
+ *
+ * Reboot API configuration
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER );
+
+#include <config/defaults.h>
+
+#include <config/local/reboot.h>
+
+#endif /* CONFIG_REBOOT_H */