ASoC: wcd-spi: Move one time initializations to component bind

One time initializations like regmap and debugfs init are currently
done in the init function. But, in case of subsystem restart, the
driver can get de-initialized and then initialized again. This causes
the debugfs and regmap entries to get removed and added again during
subsystem restart cases. Avoid this by moving all the one time
initialization of the driver to component bind.

Change-Id: Ideed297fde016b0623616be64875be094e688981
Signed-off-by: Bhalchandra Gajare <gajare@codeaurora.org>