Add probe support for the sh7372 SH4AL-DSP core.

The most common use case for this is when the system
boots from the ARM core in the sh7372 and uses the
SH core for application offload as a slave CPU.

May also be used to boot the sh7372 from the SH core.
Signed-off-by: NMagnus Damm <damm@opensource.se>
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>