mtkmodem: optionally use RIL_REQUEST_RADIO_POWER

Some MTK devices do not have RIL_REQUEST_RADIO_POWERON/OFF, so fall
back to generic RIL_REQUEST_RADIO_POWER here if environment variable
"OFONO_MTK_NO_POWERON_POWEROFF" is *NOT* set.

Signed-off-by: You-Sheng Yang <vicamo@gmail.com>
mtkmodem: add RIL_REQUEST_STORE_MODEM_TYPE

Signed-off-by: You-Sheng Yang <vicamo@gmail.com>
mtkmodem: support suspend/resume registration

Signed-off-by: You-Sheng Yang <vicamo@gmail.com>
gril: support RIL_REQUEST_SET_INITIAL_ATTACH_APN

Signed-off-by: You-Sheng Yang <vicamo@gmail.com>
mtkmodem: support RIL_REQUEST_SET_INITIAL_ATTACH_APN

Signed-off-by: You-Sheng Yang <vicamo@gmail.com>