mb/google/volteer: make variant_early_gpio_table weak

Declare variant_early_gpio_table() weak to allow override by variants.

BUG=b:148385924, b:150810535
TEST=none

Change-Id: Ife5e3b75256f71ecd763c4000fd2c7d7c927bb64
Signed-off-by: Nick Vaccaro <nvaccaro@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/39300
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: caveh jalali <caveh@chromium.org>
Reviewed-by: Srinidhi N Kaushik <srinidhi.n.kaushik@intel.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/google/volteer/variants/baseboard/gpio.c

@@ -452,7 +452,7 @@ const struct pad_config *__weak variant_override_gpio_table(size_t *num)
 	return NULL;
 }
 
-const struct pad_config *variant_early_gpio_table(size_t *num)
+const struct pad_config *__weak variant_early_gpio_table(size_t *num)
 {
 	*num = ARRAY_SIZE(early_gpio_table);
 	return early_gpio_table;