hwdocs: fix few warnings

bus/ptimer.rst:129: ERROR: Unexpected indentation.
bus/ptimer.rst:133: ERROR: Unexpected indentation.
bus/ptimer.rst:151: ERROR: Unexpected indentation.
bus/ptimer.rst:156: ERROR: Unexpected indentation.
bus/ptimer.rst:207: ERROR: Unexpected indentation.
bus/ptimer.rst:213: ERROR: Unexpected indentation.
bus/ptimer.rst:226: ERROR: Unexpected indentation.
display/nv03/vga-stack.rst:98: ERROR: Unexpected indentation.
display/nv03/vga-stack.rst:111: ERROR: Unexpected indentation.
display/nv03/vga-stack.rst:125: ERROR: Unexpected indentation.
display/nv03/vga-stack.rst:149: ERROR: Unexpected indentation.
io/pstraps.rst:125: ERROR: Unexpected indentation.
io/pstraps.rst:136: ERROR: Unexpected indentation.
io/pstraps.rst:146: ERROR: Unexpected indentation.

Signed-off-by: Dmitry Eremin-Solenikov <dmitry_eremin@mentor.com>
hwdocs: ReSTify fifo subdirectory

ReSTify a few documents in the fifo/ subdirectory. Also update links in
the other documents as txt files are no longer presented.

Signed-off-by: Dmitry Eremin-Solenikov <dmitry_eremin@mentor.com>