Create qemu-option.h

Create qemu-option.h

This patch creates a new header file and the corresponding implementation file
for parsing of parameter strings for options (like used in -drive). Part of
this is code moved from vl.c (so qemu-img can use it later).

The idea is to have a data structure describing all accepted parameters. When
parsing a parameter string, the structure is copied and filled with the
parameter values.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>