sandybridge/gma_lvds: support both Sandy&Ivy on one board

Sandy and Ivy Bridge processors use the same socket, and a mainboard
with the socket can support both types of CPUs. However, they use
different native graphics init code for LVDS and cause a crash if
running the wrong code.

This change detects the CPU type and then selects the right code to
run. It will add some more code in ramstage. It also merges the
{SANDY,IVY}BRIDGE_LVDS symbol to one SANDYBRIDGE_IVYBRIDGE_LVDS.

Tested on a Lenovo T520 with i7-2630qm and i7-3720qm

Signed-off-by: Iru Cai <mytbk920423@gmail.com>
Change-Id: I4624759f9c92d56d547db1ab4b9a1d611a182a91
Reviewed-on: https://review.coreboot.org/12087
Reviewed-by: Vladimir Serbinenko <phcoder@gmail.com>
Tested-by: build bot (Jenkins)

util/autoport/sandybridge.go

@@ -110,7 +110,7 @@ func (i sandybridgemc) Scan(ctx Context, addr PCIDevData) {
 	PutPCIDev(addr, "Host bridge")
 
 	/* FIXME:XX some configs are unsupported.  */
-	KconfigBool[i.variant+"BRIDGE_LVDS"] = true
+	KconfigBool["SANDYBRIDGE_IVYBRIDGE_LVDS"] = true
 
 	KconfigBool["CPU_INTEL_SOCKET_RPGA989"] = true
 	KconfigBool["NORTHBRIDGE_INTEL_"+i.variant+"BRIDGE"] = true