Update XhcWaitOpRegBit to take Timout argument as microsecond.

Signed-off-by: Elvin Li <elvin.li@intel.com>
Reviewed-by: Feng Tian <feng.tian@intel.com>


git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@15020 6f19259b-4bc3-4df7-8a09-765794883524