Added CreateFile to the FS_USER service

Tested with citra-emu/hwtests#8.
A sparse file essentially collapses all the null bytes in a file so that it doesn't take up more room on the hard-drive than it needs to. To an application, this means that those sections of a file that are sparse would be seen as all-zeroes.

In this case, the entire file would behave as an all-zero file without the disk-space needed or the time required to write null-bytes to the entire file.