mfd: max14577: Add muic prefix to regmap config

Add muic prefix to regmap config to differentiate between another regmap
config for MAX77836 PMIC node. Additionally remove unused
symbols: MAX14577_REG_INVALID and max14577_irq_source.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>