tg3: Use different macros for pci_chip_rev_id accesses

Upper case macros for various chip attributes are slightly
difficult to read and are a bit out of characterto the other
tg3_<foo> attribute functions.

Convert:

GET_ASIC_REV(tp->pci_chip_rev_id)       -> tg3_asic_rev(tp)
GET_CHIP_REV(tp->pci_chip_rev_id)       -> tg3_chip_rev(tp)

Remove:
GET_METAL_REV(tp->pci_chip_rev_id)      -> tg3_metal_rev(tp) (unused)

Add:
tg3_chip_rev_id(tp) for tp->pci_chip_rev_id so access styles
are similar to tg3_asic_rev and tg3_chip_rev.

These macros are not converted to static inline functions
because gcc (tested with 4.7.2) is currently unable to
optimize the object code it produces the same way and code
is otherwise larger.

Signed-off-by: Joe Perches <joe@perches.com>
Acked-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>