Skip form factor pins marked as NC

The gpio and gpio_irq FPGA tests run on form factor pins that are
marked as NC. This patch changes that behavior so they skip NC
pins.

Author: c1728p9

TESTS/mbed_hal_fpga_ci_test_shield/gpio/main.cpp

@@ -66,6 +66,9 @@ void gpio_inout_test()
 {
     for (int i = 0; i < form_factor->count; i++) {
         const PinName test_pin = form_factor->pins[i];
+        if (test_pin == NC) {
+            continue;
+        }
         if (pinmap_list_has_pin(restricted, test_pin)) {
             printf("Skipping gpio pin %s (%i)\r\n", pinmap_ff_default_pin_to_string(test_pin), test_pin);
             continue;

TESTS/mbed_hal_fpga_ci_test_shield/gpio_irq/main.cpp

@@ -248,6 +248,9 @@ void gpio_irq_test()
 {
     for (uint32_t i = 0; i < form_factor->count; i++) {
         const PinName test_pin = form_factor->pins[i];
+        if (test_pin == NC) {
+            continue;
+        }
         if (pinmap_list_has_pin(restricted, test_pin)) {
             printf("Skipping gpio pin %s (%i)\r\n", pinmap_ff_default_pin_to_string(test_pin), test_pin);
             continue;