clk: sunxi-ng: Move all clock types to a library

We've run into kconfig missing dependency errors in the sunxi-ng
code a couple times now. Each time the fix is to find the missing
select statement and add it to the Kconfig entry for a particular
SoC driver. Given that all this code is builtin (non-modular) we
don't need to do this complicated dependency tracking in Kconfig.
Instead we can move all the "library"ish code to be compiled as
lib-y instead of obj-y, let the linker throw away unused code in
the resulting vmlinux, and drop all the Kconfig stuff we use to
track clock types.

Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
[Maxime: added lib.a to obj-y, added the comment]
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>