b53: fix mmap register read/writes > 32 bit

b53: fix mmap register read/writes > 32 bit

For bcm63xx integrated switches, broadcom changed the data endianess
to match the system endianess. But this only applies to within one word,
which causes 48/64 bit values to be still split into their "litte endian"
groups.

E.g. 48 bit values (with 5 being the most significant byte) aligned

0x00 ..01  or   0123
0x04 2345       45..

will become

0x00 ..10 resp. 3210
0x04 5432       54..

Likewise for 64 bit values.

Signed-off-by: Jonas Gorski <jogo@openwrt.org>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@44568 3c298f89-4303-0410-b956-a3cf2f4a3e73