ArmPlatformPkg: reorganize PL011 code

The PL011 code in ArmPlatformPkg is organized in a weird way: there is
a single PL011Uart.h header file under Include/Drivers containing both
register definitions and function entry points. The PL011Uart library
itself is in Drivers/ but it is actually a library.

So let's clean this up: add a new PL011UartLib library class and associated
header file containing only the library prototypes, and move the library
itself under Library/ using a new GUID, with the register definitions moved
into a local header file.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>

ArmPlatformPkg/ArmPlatformPkg.dec

@@ -31,6 +31,9 @@
 [Includes.common]
   Include                        # Root include for the package
 
+[LibraryClasses]
+  PL011UartLib|Include/Library/PL011UartLib.h
+
 [Guids.common]
   gArmPlatformTokenSpaceGuid   = { 0x9c0aaed4, 0x74c5, 0x4043, { 0xb4, 0x17, 0xa3, 0x22, 0x38, 0x14, 0xce, 0x76 } }
   #