xhci: tegra21: WAR for incorrectly detected LFPS

xhci: tegra21: WAR for incorrectly detected LFPS

Remove part of WAR in http://git-master/r/#/c/552933/.
Add mailbox messages to support disabling/enabling LFPS from FW.
Enable U1/U2 support.

Bug 200041375

Change-Id: Ibd1a33b6daed2547a813c787d25b9376f7a69af0
Signed-off-by: TW Chiu <twchiu@nvidia.com>
Reviewed-on: http://git-master/r/602634
Reviewed-by: Automatic_Commit_Validation_User
Reviewed-by: Ajay Gupta <ajayg@nvidia.com>
Reviewed-by: WK Tsai <wtsai@nvidia.com>
GVS: Gerrit_Virtual_Submit
Reviewed-by: Jui Chang Kuo <jckuo@nvidia.com>
Reviewed-by: Ashutosh Jha <ajha@nvidia.com>
Tested-by: Ashutosh Jha <ajha@nvidia.com>