mb/siemens/mc_ehl: Disable all P-States

In order to get a reliable real-time performance disable all P-States
for all mc_ehl based mainboard.

Change-Id: I22857cc0f1476483ca82c1c872e4519e4b350ea9
Signed-off-by: Werner Zeh <werner.zeh@siemens.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/58894
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Lean Sheng Tan <lean.sheng.tan@intel.com>
Reviewed-by: Mario Scheithauer <mario.scheithauer@siemens.com>

src/mainboard/siemens/mc_ehl/mainboard.c

@@ -122,6 +122,9 @@ void mainboard_silicon_init_params(FSP_S_CONFIG *params)
 
 	/* Set maximum package C-state to PkgC0C1 */
 	params->PkgCStateLimit = 0;
+
+	/* Disable P-States */
+	params->MaxRatio = 0;
 }
 
 static void mainboard_init(void *chip_info)