CLK: Pistachio: Add PLL driver

CLK: Pistachio: Add PLL driver

Add a driver for the integer (GF40LP_LAINT) and fractional (GF40LP_FRAC)
PLLs present on Pistachio.

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/9316/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>