bnx2x: Segregate SR-IOV code

In this patch the SR-IOV code is segregated from the main bulk of
the bnx2x code. The CONFIG_BNX2X_SRIOV define is added to Broadcom's
Kconfig, and allows the elision of the building of all the SR-IOV
support code in the driver.
The define is dependant on the kernel CONFIG_PCI_IOV configuration
define.

Signed-off-by: Ariel Elior <ariele@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>