[efi] Add EFI image format and basic runtime environment

We have EFI APIs for CPU I/O, PCI I/O, timers, console I/O, user
access and user memory allocation.

EFI executables are created using the vanilla GNU toolchain, with the
EXE header handcrafted in assembly and relocations generated by a
custom efilink utility.

src/config/defaults/efi.h

@@ -0,0 +1,20 @@
+#ifndef CONFIG_DEFAULTS_EFI_H
+#define CONFIG_DEFAULTS_EFI_H
+
+/** @file
+ *
+ * Configuration defaults for EFI
+ *
+ */
+
+#define UACCESS_EFI
+#define IOAPI_EFI
+#define PCIAPI_EFI
+#define CONSOLE_EFI
+#define TIMER_EFI
+#define NAP_EFIX86
+#define UMALLOC_EFI
+
+#define	IMAGE_EFI		/* EFI image support */
+
+#endif /* CONFIG_DEFAULTS_EFI_H */