kbuild: switch over to thin archive ...

Starting v4.13, Linux always uses thin archive instead of relocatable
ELF to combine builtin objects.

The thin archive is basically a text file that only contains paths to
object files.

As Linux commit 98ced886dd79 mentioned, this has a lot of benefits:

 - save disk space for builds

 - speed-up building a little

 - fix some issues when liking a giant executable (for example,
   allyesconfig on ARM Linux)

 - work better with dead code elimination

The last one is important for barebox because pbl highly relies on the
dead code elimination (-f{function,data}-sections and --gc-sections)
dropping symbols that are unreachable from the linker's entry point.
The dead code elimination does not work if the same symbol names are
used in the pevious incremental link mechanism because the same name
symbols all go into the same section.

Commit a83c97f2a406 ("ARM: socfpga: generate smaller images when
multiple boards are selected") worked around it by giving a dedicate
section to each of the same name symbols. This workaround can go away.

built-in.o was renamed to built-in.a since it is now an archive.
built-in-pbl.o was renamed to built-in.pbl.a for consistency.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

kbuild: prefix compiler flag variables with KBUILD_ ...

In old days, Linux also used to use well-known variables such CFLAGS,
CPPFLAGS, etc.

They were prefixed with KBUILD_ presumably for preventing users from
overriding them accidentally.

Rename as follows:
  CFLAGS          ->  KBUILD_CFLAGS
  AFLAGS          ->  KBUILD_AFLAGS
  CPPFLAGS        ->  KBUILD_CPPFLAGS
  LDFLAGS         ->  KBUILD_LDFLAGS
  HOSTCFLAGS      ->  KBUILD_HOSTCFLAGS
  HOSTCXXFLAGS    ->  KBUILD_HOSTCXXFLAGS
  HOSTLDFLAGS     ->  KBUILD_HOSTLDFLAGS
  HOST_LOADLIBES  ->  KBUILD_HOSTLDLIBS

HOSTCFLAGS, HOSTCXXFLAGS, HOSTLDFLAGS, HOSTLDLIBS are re-used to allow
users to pass-in additional flags to the host compiler.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

kvx: Add support for device tree ...

Add dts folder with minimal device tree for kalray K200 board.

Signed-off-by: Clement Leger <cleger@kalray.eu>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

kvx: Initial Kalray Coolidge (kv3) architecture support ...

Add kalray coolidge arch/ support.

Signed-off-by: Clement Leger <cleger@kalray.eu>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>