extcon: Block the bit masking operation for cable state except for extcon core

This patch restrict the usage of extcon_update_state() in the extcon
core because the extcon_update_state() use the bit masking to change
the state of external connector. When this function is used in device drivers,
it may occur the probelm with the handling mistake of bit masking.

Also, this patch removes the extcon_get/set_state() functions because these
functions use the bit masking which is reluctant way. Instead, extcon
provides the extcon_set/get_cable_state_() functions.

Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>