MdeModulePkg/Usb: Adjust TPL to not block async transfer during usb enum.

MdeModulePkg/Usb: Adjust TPL to not block async transfer during usb enum.

EDKII usb stack is using a TPL_CALLBACK timer to monitor async transfer
request and signal event if it's done. As usb enumeration and usb mass
storage block i/o read/write runs on TPL_CALLBACK and TPL_NOTIFY level
respectively, It blocks usb async transfer requests, usually usb mouse
/use kb, getting time to run.

Without this change, user couldn't get usb mouse/kb state in time (will
show a little lag from UI view) when there is other usb transactions, such
as a new usb device inserted.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Feng Tian <feng.tian@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18169 6f19259b-4bc3-4df7-8a09-765794883524