configs/arm_foundationv8: bump to Linux 4.4.3

Bump to the latest kernel with DT path adjustment because Linux
commit ca5b34100c57 ("dts, arm64: Move dts files to vendor subdirs")
moved the DT file to the vendor sub-directory.

This commit was tested with the latest model (FVP v8 Foundation
Platform 9.5 build 41), so I updated the instruction in readme.txt
corresponding to it.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>