pmaports.cfg: add supported_heimdall_depends

Add the new variable, similar to supported_fastboot_depends.

Related: https://lists.sr.ht/~postmarketos/pmbootstrap-devel/patches/36815
Related: https://wiki.postmarketos.org/wiki/Pmaports.cfg_reference

pmaports.cfg

@@ -10,3 +10,4 @@ supported_install_boot_label=pmOS_i_boot
 supported_mkinitfs_without_flavors=True
 supported_arches=x86_64,x86,aarch64,armv7,armhf
 supported_fastboot_depends=android-tools
+supported_heimdall_depends=heimdall,android-tools