configs/nitrogen8mp: update device trees list

- remove the A0 device tree as this (pre-prod) version of the CPU isn't
supported any longer
- add '-m4' variant to enable remoteproc api to Cortex-M core
- add ENC variants for our ENC carrier [1] (+ 1 with tc358743 support)

[1]
https://boundarydevices.com/product/nitrogen8m-plus-enc-carrier-board/

Signed-off-by: Gary Bisson <gary.bisson@boundarydevices.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

configs/nitrogen8mp_defconfig

@@ -54,5 +54,5 @@ BR2_LINUX_KERNEL_CUSTOM_TARBALL_LOCATION="https://github.com/boundarydevices/lin
 BR2_LINUX_KERNEL_DEFCONFIG="boundary"
 BR2_LINUX_KERNEL_DTS_SUPPORT=y
 BR2_LINUX_KERNEL_INSTALL_TARGET=y
-BR2_LINUX_KERNEL_INTREE_DTS_NAME="freescale/imx8mp-nitrogen8mp freescale/imx8mp-a0-nitrogen8mp"
+BR2_LINUX_KERNEL_INTREE_DTS_NAME="freescale/imx8mp-nitrogen8mp freescale/imx8mp-nitrogen8mp-m4 freescale/imx8mp-nitrogen8mp-enc freescale/imx8mp-nitrogen8mp-enc-tc358743"
 BR2_LINUX_KERNEL_NEEDS_HOST_OPENSSL=y