atsam: Add get_pclock_frequency() helper function

Add get_pclock_frequency() and use it to calculate peripheral clocks.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

src/atsam/main.c

@@ -56,6 +56,13 @@ enable_pclock(uint32_t id)
         PMC->PMC_PCER1 = 1 << (id - 32);
 }
 
+// Return the frequency of the given peripheral clock
+uint32_t
+get_pclock_frequency(uint32_t id)
+{
+    return CONFIG_CLOCK_FREQ;
+}
+
 
 /****************************************************************
  * Resets