EmbeddedPkg/RealTimeClockRuntimeDxe: Improve GetWakeupTime
    
    GetWakeupTime should return full time information, including
    the daylight/timezone. Make use of the existing non-volatile
    variables for that purpose. Moreover add an error checking
    of possibly invalid parameters.
    This partially fixes FWTS and SCT Set/GetWakeupTime tests on
    Marvell platforms.
    
    Signed-off-by: Marcin Wojtas <mw@semihalf.com>
    Reviewed-by: Ard Biesheuvel <ardb@kernel.org>