anv/cmd_buffer: Reuse gen8 Cmd{Set, Reset}Event on gen7

anv/cmd_buffer: Reuse gen8 Cmd{Set, Reset}Event on gen7

Modern DXVK requires event support [1], but looks like it only
uses vkCmdSetEvent() + vkGetEventStatus(). So we can just
borrow the relevant code from gen8, leaving CmdWaitEvents still
unimplemented.

[1] https://github.com/doitsujin/dxvk/commit/8c3900c533d83d12c970b905183d17a1d3e8df1f

v2: Also move CmdWaitEvents into genX_cmd_buffer.c (Jason)

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>