MdeModulePkg/SdMmcPciHcDxe: Add SwitchClockFreqPost to SdMmcOverride

MdeModulePkg/SdMmcPciHcDxe: Add SwitchClockFreqPost to SdMmcOverride

Some SD Host Controlers need to do additional operations after clock
frequency switch.

This patch add new callback type to NotifyPhase of the SdMmcOverride
protocol. It is called after SdMmcHcClockSupply.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Marcin Wojtas <mw@semihalf.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Hao Wu <hao.a.wu@intel.com>