mlx4_core: Add second capabilities flags field

This patch adds a 64-bit flags2 features member to struct mlx4_dev to
export further features of the hardware.  The original flags field
tracks features whose support bits are advertised by the firmware in
offsets 0x40 and 0x44 of the query device capabilities command.
flags2 will track features whose support bits are scattered at various
offsets.

RSS support is the first feature to be exported through flags2.  RSS
capabilities are located at offset 0x2e.  The size of the RSS
indirection table is also given in this offset.

Signed-off-by: Shlomo Pongratz <shlomop@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>