i2c: core: Export bus recovery functions

i2c: core: Export bus recovery functions

Current -next fails to link an ARM allmodconfig because drivers that use
the core recovery functions can be built as modules but those functions
are not exported:

ERROR: "i2c_generic_gpio_recovery" [drivers/i2c/busses/i2c-davinci.ko] undefined!
ERROR: "i2c_generic_scl_recovery" [drivers/i2c/busses/i2c-davinci.ko] undefined!
ERROR: "i2c_recover_bus" [drivers/i2c/busses/i2c-davinci.ko] undefined!

Add exports to fix this.

Fixes: 7cad1e77116d3 (i2c: Add bus recovery infrastructure)
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>