Use cache path similar to DXVK

[sewnie]

Currently, in DXVK-Sarek and older versions of DXVK, DXVK_STATE_CACHE_PATH had to be specified to where the DXVK cache should be stored. In newer versions of DXVK, the cache path is automatically stored in the wineprefix or on the users cache directory:

https://github.com/doitsujin/dxvk/blob/master/README.md?plain=1#L94

Implementing this similar to DXVK would result in cleaner PWDs.