feat(imx8m): enable conditional build for SDEI

SDEI support on imx8m is an optional feature, so
make it conditional build, not enabled by default.

Signed-off-by: Jacky Bai <ping.bai@nxp.com>
Change-Id: I6e7e8d77959ea352bc019f8468793992ec7ecfc4
3 files changed