xenfb: Add [feature|request]-raw-pointer

Writes "feature-raw-pointer" during init to indicate the backend
can pass raw unscaled values for absolute axes to the frontend.
Frontends set "request-raw-pointer" to indicate the backend should
not attempt to scale absolute values to console size.
"request-raw-pointer" is only valid if "request-abs-pointer" is
also set. Raw unscaled pointer values are in the range [0, 0x7fff]

"feature-raw-pointer" and "request-raw-pointer" added to Xen
header in commit 7868654ff7fe5e4a2eeae2b277644fa884a5031e

Signed-off-by: Owen Smith <owen.smith@citrix.com>
Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>
