mb/google/herobrine: Mask out upper bits from sku_id()

When retrieving the SKU id value through the sku_id() function in
mainboard_needs_pcie_init(), we only want the values in the lower 5
bits as we can only represent SKU id up to 27.  Everything in the
higher bits should be masked out because they are not needed.

BUG=b:254281839
BRANCH=None
TEST=Make sure that NVMe is not initialized
     Tested on a herobrine board with SKU id 0

Change-Id: I0e786ec392b5e1484cb2ff6d83a8d4fdd698950c
Signed-off-by: Shelley Chen <shchen@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/70164
Reviewed-by: Julius Werner <jwerner@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/google/herobrine/mainboard.c

@@ -91,7 +91,12 @@ static void display_startup(void)
  */
 bool mainboard_needs_pcie_init(void)
 {
-	uint32_t sku = sku_id();
+	/*
+	 * Mask out everything above the actual SKU bits We have 3 sku pins,
+	 * each tristate, so we can represent numbers up to 27, or 5 bits
+	 */
+	uint32_t sku_bits_mask = 0xff;
+	uint32_t sku = sku_id() & sku_bits_mask;
 
 	if (sku == CROS_SKU_UNKNOWN) {
 		printk(BIOS_WARNING, "Unknown SKU (%#x); assuming PCIe", sku);