Followup to HAL optimizations and delays

- Cleanups, fixes for Due HAL code.
- TC_IER is write-only. Use TC_IMR to test ISR state.

Marlin/src/lcd/dogm/ultralcd_st7920_u8glib_rrd_AVR.cpp

@@ -105,7 +105,7 @@ static void ST7920_SWSPI_SND_8BIT(uint8_t val) {
 #if DOGM_SPI_DELAY_US > 0
   #define U8G_DELAY() DELAY_US(DOGM_SPI_DELAY_US)
 #else
-  #define U8G_DELAY() u8g_10MicroDelay()
+  #define U8G_DELAY() DELAY_US(10)
 #endif
 
 #define ST7920_CS()              { WRITE(ST7920_CS_PIN,1); U8G_DELAY(); }