microblaze: move "... is ready" messages to arch/microblaze/Makefile

To prepare for more fixes, move this to arch/microblaze/Makefile.
Otherwise, the same "... is ready" would be printed multiple times.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>