ARM: dts: Add clksel node for am3 gfx

Let's add a clksel node for the component clocks to avoid devicetree
unique_unit_address warnings. The component clocks can now get IO address
from the parent clksel node.

Cc: Stephen Boyd <sboyd@kernel.org>
Cc: Tero Kristo <kristo@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Message-Id: <20220204073333.18175-3-tony@atomide.com>