ARM: dts: aspeed: Make G4 clocks fixed

We do not yet have a clk driver upstream. So that users can boot the
unmodified upstream kernel, add fixed-clock and clock-frequency
properties to all of the clocks.

The values are taken from the Palmetto system. This is the only upstream
dts. It also happens to match all of the systems seen so far.

Acked-by: Cédric Le Goater <clg@kaod.org>
Acked-by: Andrew Jeffery <andrew@aj.id.au>
Signed-off-by: Joel Stanley <joel@jms.id.au>