msm: clock-local: Cleanup function naming conventions

Rename the family of functions with the 'local_clk' prefix to
have an 'rcg_clk' prefix instead, so that the function names
matche the type of clock (and type of struct) those functions
operate on.

This also helps to disambiguate these functions from other
functions that operate on different types of "local clocks"
(ie. branches, PLLs, etc).

Signed-off-by: Matt Wagantall <mattw@codeaurora.org>