LED: Introduce LED blinking pattern code

It might be useful to display some different blinking patterns to
indicate specific system state (such as DFU mode vs. regular firmware)
diff --git a/firmware/libboard/common/source/board_lowlevel.c b/firmware/libboard/common/source/board_lowlevel.c
index 5865d1d..98eb74d 100644
--- a/firmware/libboard/common/source/board_lowlevel.c
+++ b/firmware/libboard/common/source/board_lowlevel.c
@@ -127,9 +127,9 @@
 	    	      SUPC_SMMR_SMRSTEN_ENABLE;

 

     /* enable both LED and green LED */

-    PIOA->PIO_PER |= LED_RED | LED_GREEN;

-    PIOA->PIO_OER |= LED_RED | LED_GREEN;

-    PIOA->PIO_CODR |= LED_RED | LED_GREEN;

+    PIOA->PIO_PER |= PIO_LED_RED | PIO_LED_GREEN;

+    PIOA->PIO_OER |= PIO_LED_RED | PIO_LED_GREEN;

+    PIOA->PIO_CODR |= PIO_LED_RED | PIO_LED_GREEN;

 

     /* Set 3 FWS for Embedded Flash Access */

     EFC->EEFC_FMR = EEFC_FMR_FWS(3);

@@ -169,7 +169,7 @@
 #endif

 

     /* disable the red LED after main clock initialization */

-    PIOA->PIO_SODR = LED_RED;

+    PIOA->PIO_SODR = PIO_LED_RED;

 

     /* "switch" to main clock as master clock source (should already be the case */

     PMC->PMC_MCKR = (PMC->PMC_MCKR & ~(uint32_t)PMC_MCKR_CSS_Msk) | PMC_MCKR_CSS_MAIN_CLK;