Touch activation screen shown up fix

During the time of OTA activation screen startup, the app needs
to get MIN by calling getCdmaMin(). The issue in current code is that
OTA app calls getCdmaMin() before framework gets MIN data from lower
layer.

To fix this issue, framework will be providing the following new APIs
to applications for checking if MIN data is ready:
1. isMinInfoReady():
   Check if mMin variable in getCdmaMin() has been assigned a non-null value.
2. registerForSubscriptionInfoReady():
   Apps uses this API to register for notification.
3. unregisterForSubscriptionInfoReady():
   This API is used by apps to unregister notification.

Framework will be sending out the notification in the following situations:
1. when mMin is assigned a non-null MIN value;
2. When app calls register API and MIN is ready.