soc/intel/apollolake: add 4Gb and 6Gb dram density

This patch adds 4gb and 6gb dram density support to APL and GLK.

BUG=b:178665760
BRANCH=NONE
TEST=build fw and flash to the dut, the dut can boot up successfully.

Change-Id: Ic0d5d14f26a30da7a9caf4ef43d7fac88a4d2bf1
Signed-off-by: Jamie Chen <jamie.chen@intel.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/55153
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: Karthik Ramasubramanian <kramasub@google.com>
Reviewed-by: Nick Vaccaro <nvaccaro@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/intel/apollolake/include/soc/meminit.h

@@ -51,6 +51,8 @@ enum {
 
 /* LPDDR4 module density in bits. */
 enum {
+	LP4_4Gb_DENSITY = 4,
+	LP4_6Gb_DENSITY = 6,
 	LP4_8Gb_DENSITY = 8,
 	LP4_12Gb_DENSITY = 12,
 	LP4_16Gb_DENSITY = 16,

src/soc/intel/apollolake/meminit.c

@@ -278,6 +278,12 @@ void meminit_lpddr4_enable_channel(FSP_M_CONFIG *cfg, int logical_chan,
 	int fsp_rank_density;
 
 	switch (rank_density_gb) {
+	case LP4_4Gb_DENSITY:
+		fsp_rank_density = 0;
+		break;
+	case LP4_6Gb_DENSITY:
+		fsp_rank_density = 1;
+		break;
 	case LP4_8Gb_DENSITY:
 		fsp_rank_density = 2;
 		break;