MdeModulePkg/SdMmcPciHcDxe: Fix SdMmcHcReset to set only necesery bits

MdeModulePkg/SdMmcPciHcDxe: Fix SdMmcHcReset to set only necesery bits

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1185

SdMmcHcReset used to set all bits of Software Reset Register to 1
including reserved ones, which on some controllers may result in
timeout.

Now only first bit is set, which means "Software Reset for All".

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