sunxi nand: make compat partition names bootable.

There are at least three functions that format partition names in the
kernel and at least two partioin enumerators.

In addition to add_partition() make name_to_dev_t(), disk_name() and
put_partition() sunxi compat name aware.

The check is hardcoded to strcmp(name,"nand") but since no other name
than nanda..nando is required for compat this should be good enough.

v2: move the nand check before trailing partno check

Thanks Jari Helaakoski <tekkuli@gmail.com> for testing

Signed-off-by: Michal Suchanek <hramrach@gmail.com>