MIPS: Fix address type used for early memory detection.

In 'early_parse_mem' the data type used for the start
and size of a memory region specified on the command line
is incorrect. If 64-bit addressing is used, the value
gets truncated.

Signed-off-by: Steven J. Hill <Steven.Hill@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/8456/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>