x86: Add quick TSC calibration via PIT

Use the same way that Linux does for quick TSC calibration via PIT.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
crownbay: Remove hard coded CONFIG_SYS_X86_TSC_FREQ_MHZ

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>