soc/ti/am335x/cbmem.c: Use MiB macro

Use "* MiB" instead of "<< 20".

Change-Id: Iab6592804961a34fae6dc8012bfbc70023421a49
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/61332
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>

src/soc/ti/am335x/cbmem.c

@@ -1,9 +1,10 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 
 #include <cbmem.h>
+#include <commonlib/bsd/helpers.h>
 #include <symbols.h>
 
 void *cbmem_top_chipset(void)
 {
-	return _dram + (CONFIG_DRAM_SIZE_MB << 20);
+	return _dram + CONFIG_DRAM_SIZE_MB * MiB;
 }