sparc,leon: CONFIG_SPARC_LEON option and leon specific files.

The macro CONFIG_SPARC_LEON will shield, if undefined, the sun-sparc
code from LEON specific code. In
particular include/asm/leon.h will get empty through #ifdef and
leon_kernel.c and leon_mm.c will not be compiled.

Signed-off-by: Konrad Eisele <konrad@gaisler.com>
Reviewed-by:   Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: David S. Miller <davem@davemloft.net>