CLK: Pistachio: Register system interface gate clocks

Register the system interface gate clocks provided by the peripheral
general control block.  These clocks gate register access for various
peripherals.

Signed-off-by: Damien Horsley <Damien.Horsley@imgtec.com>
Signed-off-by: Andrew Bresticker <abrestic@chromium.org>
Cc: Mike Turquette <mturquette@linaro.org>
Cc: Stephen Boyd <sboyd@codeaurora.org>
Cc: devicetree@vger.kernel.org
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Cc: Ezequiel Garcia <ezequiel.garcia@imgtec.com>
Cc: James Hartley <james.hartley@imgtec.com>
Cc: James Hogan <james.hogan@imgtec.com>
Acked-by: Stephen Boyd <sboyd@codeaurora.org>
Patchwork: https://patchwork.linux-mips.org/patch/9322/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>