EmbeddedPkg/Lan9118Dxe: Use LAN9118 MMIO wrappers

EmbeddedPkg/Lan9118Dxe: Use LAN9118 MMIO wrappers

Migrate the existing code to use the new LAN9118 MMIO wrappers, ensuring
that timing requirements are respected.

The newly redundant stalls will be removed in a subsequent patch.

Cc: Leif Lindholm <leif.lindholm@linaro.org>
Cc: Ryan Harkin <ryan.harkin@linaro.org>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>