Platform/Socionext: Fix build break for SynQuacerEvalBoard

BdsDxe depends on VariablePolicyHelperLib, so move it out from
VariableRuntimeDxe.inf and add it to LibraryClasses.DXE_DRIVER and
LibraryClasses.DXE_RUNTIME_DRIVER.

This is required to fix the build break in SynQuacerEvalBoard.dsc

Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>