lib: digital_signal: digital_sequence: add furi_hal.h wrapped in ifdefs (#3964)

Per the comment at the top of the file, defining DIGITAL_SIGNAL_DEBUG_OUTPUT_PIN
to be a GpioPin variable name should allow additional debug output on
that pin. However, this would not work without modifying the file as
well to add the furi_hal.h header. Wrap including that header in the
same macro define to automatically include it when used.

Fixes: d92b0a8 ("NFC refactoring (#3050)")

Signed-off-by: Kris Bahnsen <[email protected]>
Co-authored-by: hedger <[email protected]>

Author: kbembedded

lib/digital_signal/digital_sequence.c

@@ -15,6 +15,9 @@
  * Example:
  * ./fbt --extra-define=DIGITAL_SIGNAL_DEBUG_OUTPUT_PIN=gpio_ext_pb3
  */
+#ifdef DIGITAL_SIGNAL_DEBUG_OUTPUT_PIN
+#include <furi_hal.h>
+#endif
 
 #define TAG "DigitalSequence"