lightnvm: refactor phys addrs type to u64

For cases where CONFIG_LBDAF is not set. The struct ppa_addr exceeds its
type on 32 bit architectures. ppa_addr requires a 64bit integer to hold
the generic ppa format. We therefore refactor it to u64 and
replaces the sector_t usages with u64 for physical addresses.

Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@fb.com>