[FEATURE: #148

] userspace/tools/wrs_ext_pps_latency: Support aligning the PPS out to PPS input in GM

1. Add new paramter CONFIG_EXT_PPS_LATENCY_PS in dot-config.
   Calibration 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. (deleted from the commit)
   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.

Signed-off-by: Adam Wujek <dev_public@wujek.eu>