[NVPTX] Disable DWARF .file directory for PTX

Default behavior for .file directory was changed in D105856, but
ptxas (CUDA 11.5 release) refuses to parse it:

    $ llc -march=nvptx64 llvm/test/DebugInfo/NVPTX/debug-file-loc.ll
    $ ptxas debug-file-loc.s
    ptxas debug-file-loc.s, line 42; fatal   : Parsing error near
    '"foo.h"': syntax error

Added a new field to MCAsmInfo to control default value of
UseDwarfDirectory. This value is used if -dwarf-directory command line
option is not specified.

Differential Revision: https://reviews.llvm.org/D121299