soc/amd/common: Don't program GPIOs if the table isn't set

Currently, there's no check for the table being programmed.  This skips
programming a table if the table size is zero, or the pointer to the
table has been set to NULL.

BUG=None
TEST=Set table pointer to NULL, table doesn't run.
BRANCH=Zork

Signed-off-by: Martin Roth <martinroth@chromium.org>
Change-Id: I7d09b47e7d619428b64cc0695f220fb64c71ef4c
Reviewed-on: https://review.coreboot.org/c/coreboot/+/47307
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>
Reviewed-by: Furquan Shaikh <furquan@google.com>

src/soc/amd/common/block/gpio_banks/gpio.c

@@ -187,6 +187,8 @@ void program_gpios(const struct soc_amd_gpio *gpio_list_ptr, size_t size)
 	size_t gev_items;
 	const bool can_set_smi_flags = !(CONFIG(VBOOT_STARTS_BEFORE_BOOTBLOCK) &&
 			ENV_SEPARATE_VERSTAGE);
+	if (!gpio_list_ptr || !size)
+		return;
 
 	/*
 	 * Disable blocking wake/interrupt status generation while updating