parisc: Show error if wrong 32/64-bit compiler is being used

It happens quite often that people use the wrong compiler to build the
kernel:

make ARCH=parisc   -> builds the 32-bit kernel
make ARCH=parisc64 -> builds the 64-bit kernel

This patch adds a sanity check which errors out with an instruction how
use the correct ARCH= option.

Signed-off-by: Helge Deller <deller@gmx.de>
Cc: stable@vger.kernel.org # v5.15+