ArmPlatformPkg: Fix Ecc error 10006 in ArmPlatformPkg.dsc

ArmPlatformPkg: Fix Ecc error 10006 in ArmPlatformPkg.dsc

This patch fixes the following Ecc reported error:
There should be no unnecessary inclusion of library
classes in the INF file

This comes with the additional information:
"The Library Class [TimeBaseLib] is not used
in any platform"
"The Library Class [PL011UartClockLib] is not used
in any platform"
"The Library Class [PL011UartLib] is not used
in any platform"

Indeed, the PL011SerialPortLib module requires the
PL011UartClockLib and PL011UartLib libraries.
The PL031RealTimeClockLib module requires the TimeBaseLib
library.
ArmPlatformPkg/ArmPlatformPkg.dsc builds the two modules,
but doesn't build the required libraries. This patch adds
the missing libraries to the [LibraryClasses.common] section.

Signed-off-by: Pierre Gondois <Pierre.Gondois@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@arm.com>