Make 'Format as portable' scrollable

ScrollView can't work within CoordinatorLayout,
replace it with NestedScrollView.

Bug: 213559304
Test: manual
    1. Create virtual disk by below command.
         adb shell sm set-virtual-disk true
    2. Settings -> Storage -> select the virtual disk.
    3. Format it as Phone storage.
    4. Click option menu -> Format as portable.
Change-Id: Ie5e51fb3c52431e1c94c2bcaaeb88fc05dfc993d