ARM: dts: Use clock-output-names for am4

With the TI clocks supporting the use of clock-output-names devicetree
property, we no longer need to use non-standard node names for clocks.

Cc: Stephen Boyd <sboyd@kernel.org>
Cc: Tero Kristo <kristo@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Message-Id: <20220204081529.57694-1-tony@atomide.com>