distro_bootcmd: call EFI bootmgr even without having /EFI/boot

Currently, the EFI bootmgr is only called if there is a EFI binary
inside the path for removable media is found, i.e. /EFI/boot/. This
doesn't make sense. It is the duty of the bootmgr to find out the
path and name of the EFI binary to boot. It should be called even
if there is no /EFI/boot directory.

Thus, call the bootmgr before we try to boot the EFI binary inside
the removable media path.

Also remove the ${fdtcontroladdr} parameter because the fallback is
handled in cmd/bootefi.c and that already takes care of correct settings
if the board has ACPI and thus no device tree at all.

Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>