Rewrite the miiphybb (Bit-banged MII bus driver) in order to support an arbitrary...

Rewrite the miiphybb (Bit-banged MII bus driver) in order to support an arbitrary number of mii buses.

This feature is useful when your board uses different mii buses for different
phys and all (or a part) of these buses are implemented via bit-banging mode.

The driver requires that the following macros should be defined into the board
configuration file:

CONFIG_BITBANGMII       - Enable the miiphybb driver
CONFIG_BITBANGMII_MULTI - Enable the multi bus support

If the CONFIG_BITBANGMII_MULTI is not defined, the board's config file needs
to define at least the following macros:

MII_INIT      - Generic code to enable the MII bus (optional)
MDIO_DECLARE  - Declaration needed to access to the MDIO pin (optional)
MDIO_ACTIVE   - Activate the MDIO pin as out pin
MDIO_TRISTATE - Activate the MDIO pin as input/tristate pin
MDIO_READ     - Read the MDIO pin
MDIO(v)       - Write v on the MDIO pin
MDC_DECLARE   - Declaration needed to access to the MDC pin (optional)
MDC(v)        - Write v on the MDC pin

The previous macros make the driver compatible with the previous version
(that didn't support the multi-bus).

When the CONFIG_BITBANGMII_MULTI is also defined, the board code needs to fill
the bb_miiphy_buses[] array with a record for each required bus and declare
the bb_miiphy_buses_num variable with the number of mii buses.
The record (struct bb_miiphy_bus) has the following fields/callbacks (see
miiphy.h for details):

char name[]            - The symbolic name that must be equal to the MII bus
                         registered name
int (*init)()          - Initialization function called at startup time (just
                         before the Ethernet initialization)
int (*mdio_active)()   - Activate the MDIO pin as output
int (*mdio_tristate)() - Activate the MDIO pin as input/tristate pin
int (*set_mdio)()      - Write the MDIO pin
int (*get_mdio)()      - Read the MDIO pin
int (*set_mdc)()       - Write the MDC pin
int (*delay)()         - Delay function
void *priv             - Private data used by board specific code

The board code will look like:

struct bb_miiphy_bus bb_miiphy_buses[] = {
 { .name = miibus#1, .init = b1_init, .mdio_active = b1_mdio_active, ... },
 { .name = miibus#2, .init = b2_init, .mdio_active = b2_mdio_active, ... },
 ...
int bb_miiphy_buses_num = sizeof(bb_miiphy_buses) /
                          sizeof(bb_miiphy_buses[0]);

Signed-off-by: Luigi 'Comio' Mantellini <luigi.mantellini@idf-hit.com>
Signed-off-by: Ben Warren <biggerbadderben@gmail.com>