bootsource: add definition for i2c-eeprom, spi-nor, spi-eeprom and usb ...

Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

bootsource: add support for bootsource instance information ...

Add a C interface to set and get the bootsource instance:

    int bootsource_get_instance(void);
    void bootsource_set_instance(int instance);

Also export the shell variable "bootsource_instance".

Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

bootsource: use initcall to export bootsource location to environment ...

This way the bootsource is exported to the environment, even if unknown.

Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

bootsource: create arch independent bootsource framework ...

This patch seperates the imx independent from the arch independent code. The
following functions and enums are renamed:

- imx_bootsource() -> bootsource_get()
- imx_set_bootsource() -> bootsource_set()
- enum imx_bootsource -> enum bootsource

Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>