clk: meson-gxbb: Expose GP0 dt-bindings clock id

This patch exposes the GP0 PLL clock id in the dt bindings.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Michael Turquette <mturquette@baylibre.com>
Link: lkml.kernel.org/r/1490178747-14837-5-git-send-email-narmstrong@baylibre.com