OMAP2 clock: drop CONFIG_PARTICIPANT clock flag

It turns out that the only purpose of the CONFIG_PARTICIPANT clock
flag is to prevent omap2_clk_set_rate() and omap2_clk_set_parent()
from being executed on clocks with that flag set.  The rate-changing
component can be more directly accomplished by dropping the .set_rate
and .round_rate function pointers from those CONFIG_PARTICIPANT struct
clks.  As far as the parent-changing component is concerned, it turns
out that none of the CONFIG_PARTICIPANT clocks have multiple parent
choices, so all that is necessary is for omap2_clk_set_parent() to
bail out early if the new parent is equal to the old parent.
Implement this change and get rid of the flag, which has always had a
confusing name (it appears to be a Kconfig option, falsely).

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Richard Woodruff <r-woodruff2@ti.com>