net/mlx5: Store the global doorbell in mlx5_priv

net/mlx5: Store the global doorbell in mlx5_priv

The global doorbell is used for more than just Ethernet resources, so
move it out of mlx5e_hw_objs into a common place (mlx5_priv), to avoid
non-Ethernet modules (e.g. HWS, ASO) depending on Ethernet structs.

Use this opportunity to consolidate it with the 'uar' pointer already
there, which was used as an RX doorbell. Underneath the 'uar' pointer is
identical to 'bfreg->up', so store a single resource and use that
instead.

For CQ doorbells, care is taken to always use bfreg->up->index instead
of bfreg->index, which may refer to a subsequent UAR page from the same
ALLOC_UAR batch on some NICs.

This paves the way for cleanly supporting multiple doorbells in the
Ethernet driver.

Signed-off-by: Cosmin Ratiu <cratiu@nvidia.com>
Reviewed-by: Dragos Tatulea <dtatulea@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>