vc/amd/opensil/genoa_poc/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: I5885e9ad89ed9f0aa657c56804e98c352267267f
Reviewed-on: https://review.coreboot.org/c/coreboot/+/81092
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Varshit Pandya <pandyavarshit@gmail.com>
diff --git a/src/vendorcode/amd/opensil/genoa_poc/memmap.c b/src/vendorcode/amd/opensil/genoa_poc/memmap.c
index 39b27ec..31e6f04 100644
--- a/src/vendorcode/amd/opensil/genoa_poc/memmap.c
+++ b/src/vendorcode/amd/opensil/genoa_poc/memmap.c
@@ -110,7 +110,7 @@
 		    mem_usable);
 
 	// Account for UMA and TSEG
-	const uint32_t top_mem = ALIGN_DOWN(rdmsr(TOP_MEM).lo, 1 * MiB);
+	const uint32_t top_mem = ALIGN_DOWN(get_top_of_mem_below_4gb(), 1 * MiB);
 	if (mem_usable != top_mem)
 		reserved_ram_from_to(dev, (*idx)++, mem_usable, top_mem);