clk: Rename clk-gpio-gate.c to clk-gpio.c

The file clk-gpio-gate.c does not only contain the gate clock, but also
the mux clock. Rename the file to clk-gpio.c.

Cc: Jyri Sarha <jsarha@ti.com>
Signed-off-by: Sergej Sawazki <ce3a@gmx.de>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>