Glued On Tiles

[bigdog_golfer75]

I am a new home owner and not very experienced with anything, We removed shower doors from our bathtub and when we did a lot of the tiles along the edges chipped off with the doors. I thought about just repairing it but there are so many other places in the bathroom where the tiles have just fallen off or are cracked, I decided to remove all the tiles. After doing so, it looks as if the tiles were glued on, I'd like to just sand the walls down and paint them, There is also a white powder on the wall that is flaking off, and I don't know what it is. Is it possible for me to just sand and mud these walls or am I going to need to replace the drywall completely?