bnxt_en: Initialize context memory to the value specified by firmware.

Some chips that need host context memory as a backing store requires
the memory to be initialized to a non-zero value.  Query the
value from firmware and initialize the context memory accordingly.

Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>