xtensa: replace cpu_xtensa_init() with cpu_generic_init()

xtensa: replace cpu_xtensa_init() with cpu_generic_init()

call xtensa_irq_init() at realize time which makes
cpu_xtensa_init() like generic cpu creation function.
As result we can replace it with cpu_generic_init()
which does the same job, reducing code duplication a bit.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <1503592308-93913-16-git-send-email-imammedo@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>