spirv: extract switch parsing into its own function

v2 (Jason Ekstrand):
 - Construct a list of vtn_case objects

Signed-off-by: Karol Herbst <kherbst@redhat.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/2401>
2 files changed