MLK-18577-3 armv8: xen: add console write hypercall

MLK-18577-3 armv8: xen: add console write hypercall

Introduce console write hypercall to let Uboot could directly
output with xen console, this needs CONFIG_VERBOSE_DEBUG
enabled in xen.

Because input is not a must requirement in android VM,
and develop pvconsole needs more efforts, so let's use
this hypercall first.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
(cherry picked from commit 8836c3104a1edfe542e0c1cef6690bc9d3d842a0)
(cherry picked from commit aea71150857d4617009730683c95d858acb43392)
(cherry picked from commit 3173d3ac39bed27a3197829ea13ffce5a89b07ac)