PM / OPP: Make OPP invisible to users in Kconfig

The OPP code is an in kernel library selected by its users, there is no
no architecture code required to implement it and enabling it without a
user just increases the kernel size. Since the users select rather than
depend on it just remove the ability to directly set the option from
Kconfig.

Change-Id: I48302a6fbb4769e8280103f2a7fbfbce493493d7
Signed-off-by: Mark Brown <broonie@linaro.org>
Acked-by: Nishanth Menon <nm@ti.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Git-commit: 049d595a4db3b3a20fc252298010f0545ef659a3
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>