i2c: designware-baytrail: fix sparse warnings

There is no need to export functions that are used as the callbacks in the
struct dw_i2c_dev. Otherwise we get the following warnings:

drivers/i2c/busses/i2c-designware-baytrail.c:63:5: warning: symbol 'baytrail_i2c_acquire' was not declared. Should it be static?
drivers/i2c/busses/i2c-designware-baytrail.c:114:6: warning: symbol 'baytrail_i2c_release' was not declared. Should it be static?

While here, do few indentation fixes, remove i2c_dw_eval_lock_support() from
functions exported to the modules and redundant assignment of local sem
variable.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: David E. Box <david.e.box@linux.intel.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>