hwmon: (aspeed-pwm-tacho) Select REGMAP

The driver uses regmap and thus has to select it to avoid build
errors such as the following.

drivers/hwmon/aspeed-pwm-tacho.c:337:21: error: variable
	'aspeed_pwm_tacho_regmap_config' has initializer but incomplete type

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Acked-by: Joel Stanley <joel@jms.id.au>
Fixes: 2d7a548a ("drivers: hwmon: Support for ASPEED PWM/Fan tach")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>