imx233: fix user timer

The running count is only 16-bit wide, since the always tick
setting derives from the crystal clock at 24MHz the user timer
cannot be set lower than ~300Hz which is already too high.
Switch to the 32KHz crystal source to fix this.

Change-Id: Ie7775460b17ea7ab331738734e3d688ad5563857

firmware/export/imx233.h

@@ -61,8 +61,8 @@
 #define FRAME_PHYS_ADDR (DRAM_ORIG + DRAM_SIZE - TTB_SIZE - FRAME_SIZE)
 #define FRAME           ((void *)(FRAME_PHYS_ADDR - UNCACHED_DRAM_ADDR + BUFFERED_DRAM_ADDR))
 
-/* Timer runs at APBX speed which is derived from ref_xtal@24MHz */
-#define TIMER_FREQ      24000000
+/* Timer runs at 32KHz, derived from clk32k@32KHz */
+#define TIMER_FREQ      32000
 
 /* USBOTG */
 #define USB_QHARRAY_ATTR    __attribute__((section(".qharray"),nocommon,aligned(2048)))

firmware/target/arm/imx233/timer-imx233.c

@@ -58,7 +58,7 @@ bool timer_set(long cycles, bool start)
 bool timer_start(IF_COP_VOID(int core))
 {
     imx233_setup_timer(USER_TIMER_NR, true, timer_cycles,
-        HW_TIMROT_TIMCTRL__SELECT_TICK_ALWAYS, HW_TIMROT_TIMCTRL__PRESCALE_1,
+        HW_TIMROT_TIMCTRL__SELECT_32KHZ_XTAL, HW_TIMROT_TIMCTRL__PRESCALE_1,
             false, &timer_fn);
     return true;
 }