timer: Add CONFIG_TSC_TIMER build option to disable the CPU TSC timer

timer: Add CONFIG_TSC_TIMER build option to disable the CPU TSC timer

Allow users to remove the CPU timestamp counter support at compile
time.  The PMTIMER is frequently used instead of the TSC and this
compile time option allows one to strip a few bytes from the final
binary.  This change also defaults the internal timer to use the PIT
based timer until the PMTIMER or TSC is detected.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>