firmware: imx: misc: Align imx sc msg structs to 4

The imx SC api strongly assumes that messages are composed out of
4-bytes words but some of our message structs have odd sizeofs.

This produces many oopses with CONFIG_KASAN=y:

    BUG: KASAN: stack-out-of-bounds in imx_mu_send_data+0x108/0x1f0

It shouldn't cause an issues in normal use because these structs are
always allocated on the stack.

Fixes: 15e1f2bc ("firmware: imx: add misc svc support")
Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>