bnxt_en: Fix error recovery for 5760X (P7) chips

During error recovery, such as AER fatal error slot reset, we call
bnxt_try_map_fw_health_reg() to try to get access to the health
register to determine the firmware state.  Fix
bnxt_try_map_fw_health_reg() to recognize the P7 chip correctly
and set up the health register.

This fixes this type of AER slot reset failure:

bnxt_en 0000:04:00.0: AER: PCIe Bus Error: severity=Uncorrectable (Fatal), type=Inaccessible, (Unregistered Agent ID)
bnxt_en 0000:04:00.0 enp4s0f0np0: PCI I/O error detected
bnxt_en 0000:04:00.0 bnxt_re0: Handle device suspend call
bnxt_en 0000:04:00.1 enp4s0f1np1: PCI I/O error detected
bnxt_en 0000:04:00.1 bnxt_re1: Handle device suspend call
pcieport 0000:00:02.0: AER: Root Port link has been reset (0)
bnxt_en 0000:04:00.0 enp4s0f0np0: PCI Slot Reset
bnxt_en 0000:04:00.0: enabling device (0000 -> 0002)
bnxt_en 0000:04:00.0: Firmware not ready
bnxt_en 0000:04:00.1 enp4s0f1np1: PCI Slot Reset
bnxt_en 0000:04:00.1: enabling device (0000 -> 0002)
bnxt_en 0000:04:00.1: Firmware not ready
pcieport 0000:00:02.0: AER: device recovery failed

Fixes: a432a45b ("bnxt_en: Define basic P7 macros")
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>