sfc: Replace some literal constants with EFX_PAGE_SIZE/EFX_BUF_SIZE

sfc: Replace some literal constants with EFX_PAGE_SIZE/EFX_BUF_SIZE

Mainline commit 5b6262d0ccf759a16fabe11d904a2531125a4b71

The 'page size' for PCIe DMA, i.e. the alignment of boundaries at
which DMA must be broken, is 4KB.  Name this value as EFX_PAGE_SIZE
and use it in efx_max_tx_len().  Redefine EFX_BUF_SIZE as
EFX_PAGE_SIZE since its value is also a result of that requirement,
and use it in efx_init_special_buffer().

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Orabug: 14769994
Signed-off-by: Chuck Anderson <chuck.anderson@oracle.com>
(cherry picked from commit 0d66c9ee8813a35eb5ce78ac0b2fb0286cd088ea)

Conflicts:
	drivers/net/sfc/nic.h