arch/x86/car.ld: Account for FSP-T reserved area

Tested
 - on ocp/deltalake: boots (with FSP-T).
 - qemu/i440fx: BUILD_TIMELESS=1 results in the same binary.

Change-Id: I7e364ab039b65766eb95538db6b3507bbfbfb487
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/49084
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/drivers/intel/fsp2_0/Kconfig

@@ -117,6 +117,15 @@ config FSP_CAR
 	help
 	  Use FSP APIs to initialize & Tear Down the Cache-As-Ram
 
+config FSP_T_RESERVED_SIZE
+	hex
+	default 0x100 if FSP_CAR
+	default 0x0
+	help
+	  This is the size of the area reserved by FSP-T. This is not
+	  defined in the FSP specification but in the SOC integration
+	  guides.
+
 config FSP_M_XIP
 	bool
 	default n