soc/intel: Replace `SA_PCIEX_LENGTH` Kconfig options

Use the existing `MMCONF_BUS_NUMBER` and `MMCONF_LENGTH` symbols.

Change-Id: I88dcc0d5845198f668c6604c45fd869617168231
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/50113
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
diff --git a/src/soc/intel/tigerlake/systemagent.c b/src/soc/intel/tigerlake/systemagent.c
index 29487a8..7b1813f 100644
--- a/src/soc/intel/tigerlake/systemagent.c
+++ b/src/soc/intel/tigerlake/systemagent.c
@@ -27,7 +27,7 @@
 void soc_add_fixed_mmio_resources(struct device *dev, int *index)
 {
 	static const struct sa_mmio_descriptor soc_fixed_resources[] = {
-		{ PCIEXBAR, CONFIG_MMCONF_BASE_ADDRESS, CONFIG_SA_PCIEX_LENGTH,
+		{ PCIEXBAR, CONFIG_MMCONF_BASE_ADDRESS, CONFIG_MMCONF_LENGTH,
 				"PCIEXBAR" },
 		{ MCHBAR, MCH_BASE_ADDRESS, MCH_BASE_SIZE, "MCHBAR" },
 		{ DMIBAR, DMI_BASE_ADDRESS, DMI_BASE_SIZE, "DMIBAR" },