Platforms/RaspberryPi: Switch to PcdSet##S

According to the bug:
https://bugzilla.tianocore.org/show_bug.cgi?id=2777


the deprecated code under DISABLE_NEW_DEPRECATED_INTERFACES
will be removed, which will result in compilation breakage
of the Raspberry Pi platforms. Prevent that by switching to
the different PcdSet API.

Signed-off-by: Pete Batard <pete@akeo.ie>
Reviewed-by: Leif Lindholm <leif@nuviainc.com>