d/target: Allow Variscite and BSH boards to build with missing firmware

We do not make the imx8mn DDR firmware available during the U-Boot
build, instead deferring combining these elements till image creation as
we do not want dependencies in binaries packaged in non-free repository
on packages in the target repository. This would previously buid with a
warning about the missing binaries a change upstream[1] has made this an
error unless "BINMAN_ALLOW_MISSING=1" is passed to make.

Pass this required variable for these targets.

[1]: https://source.denx.de/u-boot/u-boot/-/commit/b144b93ea9ed862468842a20dace2e465ea5ac9c



Signed-off-by: Martyn Welch <martyn.welch@collabora.com>

debian/targets.mk

@@ -41,13 +41,13 @@ ifeq (${DEB_HOST_ARCH},arm64)
 
   # Ariel D'Alessandro <ariel.dalessandro@collabora.com>
   u-boot-imx_platforms += imx8mn_bsh_smm_s2 imx8mn_bsh_smm_s2pro imx8mn_var_som
-  imx8mn_bsh_smm_s2_assigns := BL31=/usr/lib/arm-trusted-firmware/imx8mn_uart4/bl31.bin
+  imx8mn_bsh_smm_s2_assigns := BINMAN_ALLOW_MISSING=1 BL31=/usr/lib/arm-trusted-firmware/imx8mn_uart4/bl31.bin
   imx8mn_bsh_smm_s2_targets := arch/arm/dts/imx8mn-bsh-smm-s2.dtb \
     spl/u-boot-spl.bin u-boot-nodtb.bin u-boot.bin u-boot.img u-boot.itb
-  imx8mn_bsh_smm_s2pro_assigns := BL31=/usr/lib/arm-trusted-firmware/imx8mn_uart4/bl31.bin
+  imx8mn_bsh_smm_s2pro_assigns := BINMAN_ALLOW_MISSING=1  BL31=/usr/lib/arm-trusted-firmware/imx8mn_uart4/bl31.bin
   imx8mn_bsh_smm_s2pro_targets := arch/arm/dts/imx8mn-bsh-smm-s2pro.dtb \
     spl/u-boot-spl.bin u-boot-nodtb.bin u-boot.bin u-boot.img u-boot.itb
-  imx8mn_var_som_assigns := BL31=/usr/lib/arm-trusted-firmware/imx8mn_uart4/bl31.bin
+  imx8mn_var_som_assigns := BINMAN_ALLOW_MISSING=1 BL31=/usr/lib/arm-trusted-firmware/imx8mn_uart4/bl31.bin
   imx8mn_var_som_targets := arch/arm/dts/imx8mn-var-som-symphony.dtb \
     spl/u-boot-spl.bin u-boot-nodtb.bin u-boot.bin u-boot.img u-boot.itb