On r8a7791 the hardware boot mode bit MD21 indicates if hardware
debug mode is enabled or not. In case hardware debug mode is enabled
print a warning and refrain from booting secondary CPU cores.

Without this patch Koelsch with SW8-4 set to OFF will hang at SMP boot.
Signed-off-by: Magnus Damm <damm@opensource.se>
Tested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>