sparc32: implement proper LEON support in head_32 (after highmem)

We use the compatibility property to determine the
sun models. For leon we use psr.impl and ignore the
result of the getprops call.

Include a hack to allow build as the support code
is not yet converted.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Daniel Hellstrom <daniel@gaisler.com>
Cc: Konrad Eisele <konrad@gaisler.com>