drivers/intel/fsp1_1/cache_as_ram.S: Use _car_stack area for stack

Top of Temp RAM is used as bootloader stack, which is the
_car_region_end area. This area is not equal to CAR stack area as
defined in car.ld file.

Use _ecar_stack (end of CAR stack) as starting stack location.

Tested VBOOT, Vendorboot security and no security on Facebook FBG1701.

Change-Id: I16b077f60560de334361b1f0d3758ab1a5cbe895
Signed-off-by: Frans Hendriks <fhendriks@eltan.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/47737
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-by: Wim Vervoorn <wvervoorn@eltan.com>
Reviewed-by: Michał Żygowski <michal.zygowski@3mdeb.com>
Reviewed-by: Christian Walter <christian.walter@9elements.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/src/drivers/intel/fsp1_1/cache_as_ram.S b/src/drivers/intel/fsp1_1/cache_as_ram.S
index 31c3580..3be9eb9 100644
--- a/src/drivers/intel/fsp1_1/cache_as_ram.S
+++ b/src/drivers/intel/fsp1_1/cache_as_ram.S
@@ -133,7 +133,7 @@
 	jne	halt2
 
 	/* Setup bootloader stack */
-	movl	%edx, %esp
+	movl	$_ecar_stack, %esp
 
 	/*
 	 * ebp:  FSP_INFO_HEADER address