EmbeddedPkg/Lan9118Dxe: remove redundant stalls

EmbeddedPkg/Lan9118Dxe: remove redundant stalls

Now that the LAN9118-specific MMIO accessors provide the required
delays, remove the redundant stalls.

Stalls in delay loops are kept, as these give time for work to happen
beyond synchronisation of the device register file.

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>