imx8m: Guard binman nodes with CONFIG_OPTEE

imx8m: Guard binman nodes with CONFIG_OPTEE

Guard binman nodes with CONFIG_OPTEE to fix the following error
when building without optee support:

  BINMAN  .binman_stamp
Image 'image' has faked external blobs and is non-functional: tee.bin

Image 'image' is missing optional external blobs but is still functional: tee-os

/binman/section/fit/images/tee/tee-os (tee.bin):
   See the documentation for your board. You may need to build Open Portable
   Trusted Execution Environment (OP-TEE) and build with TEE=/path/to/tee.bin

Some images are invalid
make: *** [Makefile:1135: .binman_stamp] Error 103

While at it, only pass tee to the loadables lines when CONFIG_OPTEE is
defined.

Reported-by: Tim Harvey <tharvey@gateworks.com>
Signed-off-by: Fabio Estevam <festevam@denx.de>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Tested-by: Yannic Moog <y.moog@phytec.de>