Silicon/Marvell/RealTimeClockLib: make EpochSeconds, WakeupSeconds UINTN

We're going to change EfiTimeToEpoch() in edk2's TimeBaseLib to propagate
its internal UINTN calculation to the caller without an internal UINT32
truncation.

Silicon/Marvell/Armada7k8k/Library/RealTimeClockLib drives 32-bit-only
hardware, so catch any number of seconds since the epoch, from
EfiTimeToEpoch(), that doesn't fit in 32 bits.

Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Cc: Leif Lindholm <leif@nuviainc.com>
Cc: Marcin Wojtas <mw@semihalf.com>
Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Message-Id: <20201221112433.5525-1-lersek@redhat.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@arm.com>