mb/google/reef: provide override GPIO table in coral

Allow overriding specific GPIOs by SKU ID. Override two GPIO settings
for nasher to save the power consumption when the system in S0ix.

Change as below:
AVS_DMIC_CLK_A1: IGNORE -> Tx1RXDCRx0.
AVS_DMIC_CLK_B1: IGNORE -> Tx1RXDCRx0.

BUG=b:69025557
BRANCH=master
TEST=compile/verify the power consumption change from ~150mW to ~100mW
     on clamshell SKU and from ~200mW to ~100mW for convertible SKU.

Change-Id: I9e0674f206426fddb3947273754774b310106334
Signed-off-by: Chris Wang <chriswang@ami.corp-partner.google.com>
Reviewed-on: https://review.coreboot.org/22752
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

src/mainboard/google/reef/mainboard.c

@@ -29,6 +29,14 @@
 #include <variant/ec.h>
 #include <variant/gpio.h>
 
+/* override specific gpio by sku id */
+const struct pad_config __attribute__((weak))
+*variant_sku_gpio_table(size_t *num)
+{
+	*num = 0;
+	return NULL;
+}
+
 static void mainboard_init(void *chip_info)
 {
 	int boardid;
@@ -41,6 +49,9 @@ static void mainboard_init(void *chip_info)
 	pads = variant_gpio_table(&num);
 	gpio_configure_pads(pads, num);
 
+	pads = variant_sku_gpio_table(&num);
+	gpio_configure_pads(pads, num);
+
 	mainboard_ec_init();
 
 	variant_board_ec_set_skuid();