soc/intel/xeon_sp: Use generic config_t

Don't use the silicon-specific struct type to get common config
options. Instead, use the generic config_t typedef. This allows
the function to be moved to common code in upcoming patches.

Change-Id: If80b678037b4d79387e0a0f722c540df4aae2416
Signed-off-by: Marc Jones <marcjones@sysproconsulting.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/46057
Reviewed-by: Jay Talbott <JayTalbott@sysproconsulting.com>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/intel/xeon_sp/cpx/soc_acpi.c

@@ -681,7 +681,7 @@ unsigned long northbridge_write_acpi_tables(const struct device *device,
 	acpi_slit_t *slit;
 	acpi_dmar_t *dmar;
 
-	const struct soc_intel_xeon_sp_cpx_config *const config = config_of(device);
+	const config_t *const config = config_of(device);
 
 	/* SRAT */
 	current = ALIGN(current, 8);

src/soc/intel/xeon_sp/skx/soc_acpi.c

@@ -588,7 +588,7 @@ unsigned long northbridge_write_acpi_tables(const struct device *device,
 	acpi_slit_t *slit;
 	acpi_dmar_t *dmar;
 
-	const struct soc_intel_xeon_sp_skx_config *const config = config_of(device);
+	const config_t *const config = config_of(device);
 
 	/* SRAT */
 	current = ALIGN(current, 8);