clk: sprd: fix compile-testing

clk: sprd: fix compile-testing

I got a build failure with CONFIG_ARCH_SPRD=m when the
main portion of the clock driver failed to get linked into
the kernel:

ERROR: modpost: "sprd_pll_sc_gate_ops" [drivers/clk/sprd/sc9863a-clk.ko] undefined!
ERROR: modpost: "sprd_pll_ops" [drivers/clk/sprd/sc9863a-clk.ko] undefined!
ERROR: modpost: "sprd_div_ops" [drivers/clk/sprd/sc9863a-clk.ko] undefined!
ERROR: modpost: "sprd_comp_ops" [drivers/clk/sprd/sc9863a-clk.ko] undefined!
ERROR: modpost: "sprd_mux_ops" [drivers/clk/sprd/sc9863a-clk.ko] undefined!
ERROR: modpost: "sprd_gate_ops" [drivers/clk/sprd/sc9863a-clk.ko] undefined!
ERROR: modpost: "sprd_sc_gate_ops" [drivers/clk/sprd/sc9863a-clk.ko] undefined!
ERROR: modpost: "sprd_clk_probe" [drivers/clk/sprd/sc9863a-clk.ko] undefined!
ERROR: modpost: "sprd_clk_regmap_init" [drivers/clk/sprd/sc9863a-clk.ko] undefined!
ERROR: modpost: "sprd_pll_ops" [drivers/clk/sprd/sc9860-clk.ko] undefined!
ERROR: modpost: "sprd_div_ops" [drivers/clk/sprd/sc9860-clk.ko] undefined!
ERROR: modpost: "sprd_mux_ops" [drivers/clk/sprd/sc9860-clk.ko] undefined!

This is a combination of two trivial bugs:

- A platform should not be 'tristate', it should be a 'bool' symbol
  like the other platforms, if only for consistency, and to avoid
  surprises like this one.

- The clk Makefile does not traverse into the sprd subdirectory
  if the platform is disabled but the drivers are enabled for
  compile-testing.

Fixing either of the two would be sufficient to address the link failure,
but for correctness, both need to be changed.

Fixes: 4b5e849637d9 ("arm64: change ARCH_SPRD Kconfig to tristate")
Fixes: 5fd468ef0cee ("clk: sprd: Add common infrastructure")
Acked-by: Chunyan Zhang <chunyan.zhang@unisoc.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>