kconfig: syntax cleanup - drop support for "depends/requires/def_boolean"

Remove the following redundant and never or rarely used kconfig syntax:

- "def_boolean" (same as "def_bool")
- "requires" (same as "depends on")
- "depends" (same as "depends on")

This patch contains the code changes and Kconfig updates.
The shipped files are in next patch to let actual codechange stand out.

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Cc: "Randy.Dunlap" <rdunlap@xenotime.net>
Cc: Bryan Wu <bryan.wu@analog.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Dmitry Torokhov <dtor@mail.ru>
Cc: "John W. Linville" <linville@tuxdriver.com>
Cc: Roman Zippel <zippel@linux-m68k.org>
Cc: Richard Purdie <rpurdie@rpsys.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>