Compiling the tree with allyesconfig is helpful because different
compilers (gcc, clang) or static checkers (e.g. clang's scan-build)
can then process and check more code.

This patch introduces two new configuration symbols that Kconfig files
can depend on. That way, code that is only working where a cache or DMA
implementation exists can be opted out.

Signed-off-by: Holger Schurig <holgerschurig@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>