Rename mainline_system(.*).mk to generic_system(.*).mk

Rename mainline_system to generic_system in mk files
to avoid confusion with mainline module.

Bug: 160649682
Test: lunch csi_arm64 && m nothing
Test: lunch csi_x86 && m nothing
Test: lunch mgsi_arm && m nothing
Test: lunch mgsi_arm64 && m nothing
Test: lunch mgsi_x86 && m nothing
Test: lunch mgsi_x86_64 && m nothing
Change-Id: I3609ec2d91b0f08859a36cac75c25876b1db6d6a
6 files changed