Update the bcm config file system_ref_core_clock_khz param to
handlesystems with J2cplus linecards.
We need system_ref_core_clock_khz to be set to 1600000 for supporting j2
and j2cplus linecards on the same chassis.
For 7800 LCs, set LAG mode to support 1024 number of 16-member system
LAGs.
Why I did it
The SOC property changes are necessary to match #10519 which increases the number of system LAG IDs to 1024.
Description for the changelog
For 7800 LCs, set LAG mode to support 1024 number of 16-member system
LAGs.
