Make REMOTEPROC core a selectable kconfig option, and update
remoteproc client drivers to 'depends on' the core. This avoids
some nasty Kconfig recursive dependency issues. Also when using
menuconfig client drivers will be hidden until the core has been
enabled.

Documentation/kbuild/kconfig-language.txt:

  Note:
        select should be used with care. select will force
        a symbol to a value without visiting the dependencies.
        By abusing select you are able to select a symbol FOO even
        if FOO depends on BAR that is not set.
        In general use select only for non-visible symbols
        (no prompts anywhere) and for symbols with no dependencies.
        That will limit the usefulness but on the other hand avoid
        the illegal configurations all over.

Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>