kconfig: Standardize "depends" -> "depends on" in Kconfig files

Standardize the miniscule percentage of occurrences of "depends" in
Kconfig files to "depends on", and update kconfig-language.txt to
reflect that.

Signed-off-by: Robert P. J. Day <rpjday@mindspring.com>
Signed-off-by: Adrian Bunk <bunk@stusta.de>