Validate dtc is new enough

Subsequent patches assume that dtc supports various recent features.
These are available in dtc 1.4.0. Validate that dtc is at least that
version.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
---
v2: New patch.
xilinx: move microblaze-generic .dts to standard location

Aside from microblaze, all other SoCs/boards/vendors store their DT files
in board/$vendor/dts/$soc-$board.dts. Move microblaze-generic.dts to this
location for consistency.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
dts/Makefile: simplify dtc invocation

The invocation of dtc is significantly more complex that it could be,
in order to work around an issue on old versions of dtc, which print
a message to stdout every time they run.

Remove this workaround, on the assumption that people have or will
upgrade to a newer version of dtc. This simplifies the build rule
significantly.

Related, split the invocation of cpp and dtc into separate commands
rather than a pipeline, so that if either fail, it is detected. This has
the nice benefit of saving off the result of the pre-processing step,
allowing it to be easily inspected.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
dts/Makefile: unify cpp/dtc include paths

*.dts may use #include (via cpp) or /include/ (via dtc; assuming a newer
dtc). The choice is up to the creator of the DT. Create a common variable
DTC_INCDIRS that lists the paths searched by include statements, and
update cpp and dtc invocation to use them.

For cpp, also specify -nostdinc to ensure the same set of paths is
available to both type of include statement.

For dtc, create a new DTC_FLAGS variable to hold all the flags passed to
dtc.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
dt: don't use ARCH_CPU_DTS

Now that we assume dtc supports the -i option, we don't need to use
ARCH_CPU_DTS in *.dts{,i}; we simply specify the include filename
directly, and dtc will find it.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
dts/Makefile: don't define ARCH_CPU_DTS, BOARD_DTS

Now that nothing uses the defines ARCH_CPU_DTS, BOARD_DTS, stop defining
them.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
config: don't define CONFIG_ARCH_DEVICE_TREE

Now that nothing uses CONFIG_ARCH_DEVICE_TREE, stop defining it.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
dts/Makefile: don't use cpp -P

Recent dtc supports #line directives in the input source code, and even
uses them to generate useful line numbers in any messages it emits. Stop
passing -P to cpp, since there's no need any more.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
dts/Makefile: pass -undef -D__DTS__ to cpp

This brings U-Boot's cpp invocation into line with the way the Linux
kernel invokes cpp on device trees. Consistency will be useful to ensure
*.dts is portable between the two.

-undef also has the added advantage of not defining "linux", so DT
property names such as "linux,keymap" don't get mangled.

Signed-off-by: Stephen Warren <swarren@nvidia.com>