intel: Fix build of Intel DRM on x86 systems

Commit efd6e81e inadvertently broke the build by looking for "i?86" or
"x86_64" in $host_os.  The correct variable to check is $host_cpu.

This was preventing libdrm_intel.so from being built.

Reviewed-by: Chad Versace <chad.versace@linux.intel.com>