Create linux/of_platorm.h

Move common stuff from asm-powerpc/of_platform.h to here and
move the common bits from asm-sparc*/of_device.h here as well.

Create asm-sparc*/of_platform.h and move appropriate parts of
of_device.h to them.

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Acked-by: Paul Mackerras <paulus@samba.org>
Acked-by: David S. Miller <davem@davemloft.net>