Clean up the Ps2keyboardDxe module

Clean up the Ps2keyboardDxe module
1) Use MicroSecondDelay() produced by TimerLib to replace gBS->Stall
2) Add more command/register/status definition for 8042/8048 chipset and remove hard code value used in driver's source code;
3) Remove some unused function declaration before function implementation.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@8604 6f19259b-4bc3-4df7-8a09-765794883524