Implement XamContentOpenFile

[BalkoBalkho]

Implements #1247

Observed behaviour on 4D530A1A

before this commit it was not calling any Xam::nui functions,

1. it attempts to open 3 files
2. loads something, and plays its kinect tutorial video in a loop (soft lock)

Now it

1. attempts to open 3 files
2. calls XamNuiCameraTiltSetCallback_entry
3. loads for a few seconds
4. crashes in guest

This is my first xenia PR, Im unsure about adding the symlink "update" to mount directory but it seems correct.