powerpc: Merge various powermac-related header files.

Except for smu.h, which moved from asm-ppc64 to asm-powerpc, all
of these moved from asm-ppc to asm-powerpc.  In each case the
asm-ppc64 version (if there was one) was just a single line
including the asm-ppc version.
Signed-off-by: Paul Mackerras <paulus@samba.org>

include/asm-ppc64/dbdma.h

-#include <asm-ppc/dbdma.h>
-

include/asm-ppc64/keylargo.h

-#include <asm-ppc/keylargo.h>
-

include/asm-ppc64/macio.h

-#include <asm-ppc/macio.h>
-

include/asm-ppc64/pmac_feature.h

-#include <asm-ppc/pmac_feature.h>
-

include/asm-ppc64/pmac_low_i2c.h

-#include <asm-ppc/pmac_low_i2c.h>
-

include/asm-ppc64/uninorth.h

-#include <asm-ppc/uninorth.h>
-