bitbake.conf: add MACHINE to SDK_NAME

bitbake.conf: add MACHINE to SDK_NAME

Do the same here as Poky has done 5 years ago, adding MACHINE to
SDK_NAME:

https://git.yoctoproject.org/meta-yocto/commit/?id=3614dd4aee9d19f1024edb6a36b2862c2d726c04

This avoids file conflicts in deploy/sdk/ when building multiple
machines (either manually or via multiconfig), where sdk/toolchain
installers, manifests and now SPDX archives will overlap otherwise.

Signed-off-by: Denys Dmytriyenko <denys@konsulko.com>
Signed-off-by: Denys Dmytriyenko <denis@denix.org>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>