1. Add new paramter CONFIG_EXT_PPS_LATENCY_PS in dot-config. Calib-
ration is needed to align the PPS out to PPS input in GM mode.
    2. Add new variable ext_pps_latency_ps in struct spll_stats, using it
to transfer the ext_pps_latency parameter to WRPC-SW.
    3. Change SPLL_STATS_VER to 4, modify the related function.
    4. Add a new tool function: wrs_ext_pps_latency, which will change
the Main PLL phase shift in GM mode, according to the parameter
CONFIG_EXT_PPS_LATENCY_PS in dot-config. Add this new function to startup-
mb.sh, making it autostart.