[sanboot] Add "sanhook" and "sanunhook" commands

Expose the multiple-SAN-drive capability of the iPXE core via the iPXE
command line by adding commands to hook and unhook additional drives.

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

src/arch/i386/include/int13.h

@@ -261,7 +261,4 @@ struct master_boot_record {
 	uint16_t magic;
 } __attribute__ (( packed ));
 
-/** Use natural BIOS drive number */
-#define INT13_USE_NATURAL_DRIVE 0xff
-
 #endif /* INT13_H */

src/arch/i386/include/ipxe/bios_sanboot.h

@@ -15,4 +15,15 @@ FILE_LICENCE ( GPL2_OR_LATER );
 #define SANBOOT_PREFIX_pcbios __pcbios_
 #endif
 
+/**
+ * Get default SAN drive number
+ *
+ * @ret drive		Default drive number
+ */
+static inline __always_inline unsigned int
+SANBOOT_INLINE ( pcbios, san_default_drive ) ( void ) {
+	/* Default to booting from first hard disk */
+	return 0x80;
+}
+
 #endif /* _IPXE_BIOS_SANBOOT_H */