regmap: Add hook for printk logging for debugging during early init

Sometimes for failures during very early init the trace infrastructure
isn't available early enough to be used.  For this sort of problem
defining LOG_DEVICE will add printks for basic register I/O on a specific
device, allowing trace to be extracted when the trace system doesn't come
up early enough to work with.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>