oeqa/core/decorator: add decorators to skip based on HOST_ARCH

oeqa/core/decorator: add decorators to skip based on HOST_ARCH

There are already decorators to skip on the value of MACHINE, but for
flexibility it's better to skip based on the target architecture. This
means, for example, the ISO image tests could skip if the architecture
isn't x86.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
(cherry picked from commit 0c21ff0a92906b6b4820eb8beddf8762fe70653d)
Signed-off-by: Haixiao Yan <haixiao.yan.cn@windriver.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>