MIPS: Malta: Remove fw_memblock_t abstraction

The fw_getmdesc function & fw_memblock_t abstraction is only used by
Malta, and so far as I can tell serves no purpose beyond making the code
less clear than it could be. Remove the useless level of abstraction.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Cc: James Hogan <james.hogan@imgtec.com>
Cc: Markos Chandras <markos.chandras@imgtec.com>
Patchwork: https://patchwork.linux-mips.org/patch/11221/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>