net: dsa: bcm_sf2: Add support for BCM7278 integrated switch

Add support for the integrated switch found on BCM7278:

- core_reg_align is set to 1, to force a translation into the target
  address space which is 8 bytes aligned
- an alternate SWITCH_REG layout is provided since registers are largely
  bit/masks compatible but have different offsets
- conditional for all CORE_STS_OVERRIDE_{IMP,GMII_P} since those got
  moved way out of the traditional register space

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>