MdeModulePkg/Xhci: make all timeout values be consistent with comments.

MdeModulePkg/Xhci: make all timeout values be consistent with comments.

In the original code, there exists some mismatches between the real
waiting time and the corresponding timeout comments. For example, the
XHC_GENERIC_TIMEOUT comment says it's 10ms timeout value, but the real
code in fact waits 10s.

So the code is refined to be consistent in code logic and comments.

Note XHC_POLL_DELAY macro also be removed and the polling interval in
XhcWaitOpRegBit() is changed from 1ms to 1us to keep same code style
with other code. It has no real functionality impact.

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@18235 6f19259b-4bc3-4df7-8a09-765794883524