bus: tegra-aconnect: Make symbol tristate

The driver uses symbols that weren't being exported in earlier versions
of the Linux kernel and hence it had to be made bool. The exports have
been merged into v4.8-rc1, so the driver can now be built as a module
again.
Signed-off-by: Thierry Reding <treding@nvidia.com>

drivers/bus/Kconfig

@@ -132,12 +132,8 @@ config SUNXI_RSB
 	  with various RSB based devices, such as AXP223, AXP8XX PMICs,
 	  and AC100/AC200 ICs.
 
-# TODO: This uses pm_clk_*() symbols that aren't exported in v4.7 and hence
-# the driver will fail to build as a module. However there are patches to
-# address that queued for v4.8, so this can be turned into a tristate symbol
-# after v4.8-rc1.
 config TEGRA_ACONNECT
-	bool "Tegra ACONNECT Bus Driver"
+	tristate "Tegra ACONNECT Bus Driver"
 	depends on ARCH_TEGRA_210_SOC
 	depends on OF && PM
 	select PM_CLK