tegra-minimal-initramfs: add bbappend

to remove `rootfs_version_info` from ROOTFS_POSTPROCESS_COMMAND.
The scriptlet is added by mender-workarounds.bbclass, but is
not needed in the initramfs.  This allows sstate for the minimal
initramfs to be shared between mender and non-mender builds.

Signed-off-by: Matt Madison <matt@madison.systems>