MLK-19131 configs: imx8mm_evk: add jailhouse boot command

MLK-19131 configs: imx8mm_evk: add jailhouse boot command

Add jailhouse env. Currently need to pass clk_ignore_unused to bootargs
to avoid linux root cell shutdown clocks used by inmates.

If only want a minimal clk being on in inmates, the clks could
be added in clk_inits_on in linux kernel drivers/clk/imx/clk-imx8mm.c
or use init-on-array under clk node.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
(cherry picked from commit 7732b3b87423069c1c31d25ec07201098062b717)
(cherry picked from commit 718b0792dfedcf68b6c2e93d3eefe499ec463433)