drivers/xgi/z9s: Port Linux framebuffer initialization to coreboot

Add native XGI Z9s framebuffer support to coreboot
XGI initialization code largely taken from Linux 3.18.5

TEST: Booted KFSN4-DRE with XGI Volari Z9s into SeaBIOS
with SeaVGABIOS enabled.  Text appeared correctly on screen
and interaction with graphical comboot menu was successful.
However, Linux cleared the framebuffer on boot, rendering the
screen useless until Linux loaded its native xgifb driver.

Change-Id: I606a3892849fc578b0c4d74536aec0a0adef3be3
Signed-off-by: Timothy Pearson <tpearson@raptorengineeringinc.com>
Reviewed-on: http://review.coreboot.org/8331
Tested-by: build bot (Jenkins)
Reviewed-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

src/include/device/pci_ids.h

@@ -1976,6 +1976,10 @@
 #define PCI_DEVICE_ID_ALTIMA_AC1000	0x03e8
 #define PCI_DEVICE_ID_ALTIMA_AC9100	0x03ea
 
+#define PCI_VENDOR_ID_XGI		0x18ca
+#define PCI_DEVICE_ID_XGI_20		0x0020
+#define PCI_DEVICE_ID_XGI_40		0x0040
+
 #define PCI_VENDOR_ID_SYMPHONY		0x1c1c
 #define PCI_DEVICE_ID_SYMPHONY_101	0x0001