ASoC: Disable regmap helpers if regmap is disabled

If regmap is disabled there will be no users of the ASoC regmap helpers.
Furthermore regmap_exit() will no be defined causing the following compile
error:
	sound/soc/soc-core.c: In function 'snd_soc_component_exit_regmap':
	sound/soc/soc-core.c:2645:2: error: implicit declaration of function
		'regmap_exit' [-Werror=implicit-function-declaration]

So disable the helpers if regmap is disabled.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Fixes: 20feb881

 ASoC: Add helper functions for deferred regmap setup")
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@kernel.org>