buildroot

configs: bump ARC axs10x Linux kernel and headers to 4.2 release

Linux kernel 4.2 was finally released, so bumping from 4.2-rc5 to
final release.

Updating Linux headers to 4.2 branch since they are introduced in
Buildroot as well already.

Also adding 1 back-ported patch that makes SD/MMC cards usable on AXS
boards.  This patch will be a part of 4.3 (already in linux-next) and
hopefully will make its way in 4.2.1.

Once that patch appears in 4.2.x it can be removed from here.

Cc: Peter Korsgaard <peter@korsgaard.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>