ArmPlatformPkg: PL011 Dynamic clock freq Support

Some platform support dynamic clocking, which is controlled by some
jumper setting or hardware registers. Result of that is that PCD
PL011UartClkInHz would need to be updated for frequency change.

This patch implements support for dynamic frequency for PL011 uart.

This patch implements default lib, which is using Pcd. Platform which
needs dynamic clocking needs implement PL011UartClockLib

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Udit Kumar <udit.kumar@nxp.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

ArmPlatformPkg/Library/PL011UartClockLib/PL011UartClockLib.c

@@ -0,0 +1,29 @@
+/** @file
+*
+*  Copyright 2018 NXP
+*
+*  This program and the accompanying materials
+*  are licensed and made available under the terms and conditions of the BSD License
+*  which accompanies this distribution.  The full text of the license may be found at
+*  http://opensource.org/licenses/bsd-license.php
+*
+*  THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
+*  WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
+*
+**/
+
+#include <Base.h>
+
+/**
+  Return clock in for PL011 Uart IP
+
+  @return Pcd PL011UartClkInHz
+**/
+UINT32
+EFIAPI
+PL011UartClockGetFreq (
+  VOID
+  )
+{
+  return FixedPcdGet32 (PL011UartClkInHz);
+}