soc/amd/stoneyridge/memmap: use get_top_of_mem_below_4gb

Use get_top_of_mem_below_4gb instead of open-coding the functionality.

Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Change-Id: Ic673deb725a541c7535ae769f589cd82ea42a561
Reviewed-on: https://review.coreboot.org/c/coreboot/+/74614
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin Roth <martin.roth@amd.corp-partner.google.com>

src/soc/amd/stoneyridge/memmap.c

@@ -13,9 +13,7 @@
 
 uintptr_t cbmem_top_chipset(void)
 {
-	msr_t tom = rdmsr(TOP_MEM);
-
-	if (!tom.lo)
+	if (!get_top_of_mem_below_4gb())
 		return 0;
 
 	/* 8MB alignment to keep MTRR usage low */