soc: imx: Try harder to get imx8mq SoC revisions

The mainline ATF doesn't currently support the FSL_SIP_GET_SOC_INFO call
nor does it have the code to identify different imx8mq SOC revisions so
mimic what NXPs ATF does here.

As a fallback use ATF so we can identify new revisions once it gains
support or when using NXPs ATF.

Signed-off-by: Guido Günther <agx@sigxcpu.org>
2 jobs for forward-upstream/next-20191018/imx8-soc-info/v2-wip in 33 minutes and 17 seconds (queued for 32 minutes and 19 seconds)
latest
Status Job ID Name Coverage
  Build
failed #181775
librem5
build:aarch64

00:01:45

passed #181776
librem5
build:armhf

00:32:29

 
Name Stage Failure
failed
build:aarch64 Build
  HOSTCC  scripts/kconfig/symbol.o
HOSTCC scripts/kconfig/util.o
HOSTLD scripts/kconfig/conf
***
*** Can't find default configuration "arch/arm64/configs/librem5-devkit_defconfig"!
***
make[1]: *** [scripts/kconfig/Makefile:90: librem5-devkit_defconfig] Error 1
make: *** [Makefile:567: librem5-devkit_defconfig] Error 2
ERROR: Job failed: exit code 1