tg3: Break out RSS indir table init and assignment

This patch creates a new device member to hold the RSS indirection table
and separates out the code that initializes the table from the code that
programs the table into device registers.

Signed-off-by: Matt Carlson <mcarlson@broadcom.com>
Reviewed-by: Michael Chan <mchan@broadcom.com>
Reviewed-by: Benjamin Li <benli@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>