Repurpose the BNXT_FLAG_CHIP_SR2 flag by renaming it to
BNXT_FLAG_CHIP_P7 since the SR2 chip never went to production.  The SR2
statictics structure is also renamed for the P7 chip.  Define the basic
P7 doorbell bits (Epoch. Toggle, etc) and implement the Epoch bit
logic.  The next higher bit beyond the legal doorbell mask is the
Epoch bit used for doorbells on P7 chips.  This bit is used by the
chip to detect dropped doorbells.

The 57608 chip ID belonging to the P7 family is also defined.  Note
that the PCI ID is not added until the last patch in the series.
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Link: https://lore.kernel.org/r/20231201223924.26955-4-michael.chan@broadcom.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>