net/mlx5e: Preparations for supporting larger number of channels

Data center server CPUs number keeps getting larger with time.
Currently, our driver limits the number of channels to 128.

Maximum channels number is enforced and bounded by hardcoded
defines (en.h/MLX5E_MAX_NUM_CHANNELS) even though the device and machine
(CPUs num) can allow more.

Refactor current implementation in order to handle further channels.

The maximum supported channels number will be increased in the followup
patch.

Introduce RQT size calculation/allocation scheme below:
1) Preserve current RQT size of 256 for channels number up to 128 (the
   old limit).
2) For greater channels number, RQT size is calculated by multiplying
   the channels number by 2 and rounding up the result to the nearest
   power of 2. If the calculated RQT size exceeds the maximum supported
   size by the NIC, fallback to this maximum RQT size
   (1 << log_max_rqt_size).

Since RQT size is no more static, allocate and free the indirection
table SW shadow dynamically.

Signed-off-by: Adham Faris <afaris@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>