tg3: Use pci_ioremap_bar()

This patch replaces the existing APE register mapping code with a call
to pci_ioremap_bar().  The code that maps the main device register space
did not undergo a similar change because the information derived from
the pci_resource_start() and pci_resource_len() is still used to
populate the (optional) mem_start and mem_end netdevice members.
Replace hardcoded constants where appropriate.

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