clk: axi-clkgen: Remove version 1 support

Version 1 of the axi-clkgen core has not been used in new designs for over
two years now. This is a soft peripheral used in FPGAs and anybody who has
updated their kernel to the latest version will also have updated the
bitstream containing the clock generator. So it should be safe to drop
support for this now.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>