Doc: mfd: as3722: Add details of optional missing property

Add details of following properties which are used on driver but
not documented on DT binding document.
- ams,enable-internal-int-pullup
- ams,enable-internal-i2c-pullup

Reported-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>