[usb] Add support for xHCI host controllers

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

src/config/config_usb.c

 /*
  * Drag in USB controllers
  */
+#ifdef USB_HCD_XHCI
+REQUIRE_OBJECT ( xhci );
+#endif

src/config/defaults/pcbios.h

 #define	SANBOOT_PROTO_IB_SRP	/* Infiniband SCSI RDMA protocol */
 #define	SANBOOT_PROTO_FCP	/* Fibre Channel protocol */
 
+#define	USB_HCD_XHCI		/* xHCI USB host controller */
+
 #define	REBOOT_CMD		/* Reboot command */
 #define	CPUID_CMD		/* x86 CPU feature detection command */
 

src/include/ipxe/errfile.h

 #define ERRFILE_pcivpd		     ( ERRFILE_DRIVER | 0x00060000 )
 #define ERRFILE_usb		     ( ERRFILE_DRIVER | 0x00070000 )
 #define ERRFILE_usbhub		     ( ERRFILE_DRIVER | 0x00080000 )
+#define ERRFILE_xhci		     ( ERRFILE_DRIVER | 0x00090000 )
 
 #define ERRFILE_nvs		     ( ERRFILE_DRIVER | 0x00100000 )
 #define ERRFILE_spi		     ( ERRFILE_DRIVER | 0x00110000 )