ARM: dts: DRA7: Add PCIe related clock nodes

This patch adds optfclk_pciephy_clk and optfclk_pciephy_div_clk
which are used by PCIe phy. It also adds a mux clock to choose
the source of optfclk_pciephy_div_clk clock.

Signed-off-by: J Keerthy <j-keerthy@ti.com>
Signed-off-by: Tero Kristo <t-kristo@ti.com>
Tested-by: Nishanth Menon <nm@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>