linuxkpi: Move IS_ENABLED() and friends to <linux/kconfig.h>
The header is included in <linux/xarray.h> like it is on Linux. Some DRM
code depends on this header "pollution".
Reviewed by: bz
Approved by: bz
Differential Revision: https://reviews.freebsd.org/D38567
(cherry picked from commit 4b0552d5f4ea0bd09d7f0f178810886472e84d63)