arm: mach-k3: Cleanup common start_non_linux_remote_cores()

The mach-k3 common code defined a weak start_non_linux_remote_cores()
function so that the proper implementation can be plugged in the
SoC-specific source files. This won't be needed anymore, so remove the
the common code.

Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Link: https://lore.kernel.org/r/20210726211311.5977-4-s-anna@ti.com