arm: mach-k3: Move J721e SoC detection out of common section

arm: mach-k3: Move J721e SoC detection out of common section

This belongs in the J721e specific file as it is the only place
this is used. Any board level users should use the SOC driver.

While here, move the J721e and J7200 SoC IDs out of sys_proto.h
and into hardware.h. Use a macro borrowed from Rockchip and add
the rest of the SoC IDs for completeness and later use.

Signed-off-by: Andrew Davis <afd@ti.com>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>