Create "gsi_v4.0.c", "gsi_v4.5.c", and "gsi_v4.9.c" as essentially
identical copies of "gsi_v3.5.1.c".  The only difference is the name
of the exported "gsi_regs_vX_Y" structure.  The next patch will
start differentiating them.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>