ARM: keystone2: K2G: power-off DSP during boot

The DSPs are powered on by default upon a Power ON reset, and
they are powered off on current Keystone 2 SoCs - K2HK, K2L, K2E
during the boot in u-boot. This is not functional on K2G though.
Extend the existing DSP power-off support to the only DSP present
on K2G. Do note that the PSC clock domain module id for DSP on K2G
differs from that of previous Keystone2 SoCs.

Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>