types: move phys_vec definition to common header

Move the struct phys_vec definition from block/blk-mq-dma.c to
include/linux/types.h to make it available for use across the kernel.

The phys_vec structure represents a physical address range with a
length, which is used by the new physical address-based DMA mapping
API. This structure is already used by the block layer and will be
needed for DMA phys API users.

Moving this definition to types.h provides a centralized location
for this common data structure and eliminates code duplication
across subsystems that need to work with physical address ranges.

Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>