lpc176x: Introduce get_pclock_frequency()

Add get_pclock_frequency() - a standard way of obtaining the
peripheral clock frequency.

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

src/lpc176x/main.c

@@ -1,9 +1,10 @@
 // Main starting point for LPC176x boards.
 //
-// Copyright (C) 2018  Kevin O'Connor <kevin@koconnor.net>
+// Copyright (C) 2018-2021  Kevin O'Connor <kevin@koconnor.net>
 //
 // This file may be distributed under the terms of the GNU GPLv3 license.
 
+#include "autoconf.h" // CONFIG_CLOCK_FREQ
 #include "board/armcm_boot.h" // armcm_main
 #include "internal.h" // enable_pclock
 #include "sched.h" // sched_main
@@ -57,6 +58,13 @@ enable_pclock(uint32_t pclk)
     }
 }
 
+// Return the frequency of the given peripheral clock
+uint32_t
+get_pclock_frequency(uint32_t pclk)
+{
+    return CONFIG_CLOCK_FREQ;
+}
+
 // Main entry point - called from armcm_boot.c:ResetHandler()
 void
 armcm_main(void)