kbuild, modpost: fix unexpected non-allocatable warning with mips

mips emit the following debug sections:
.mdebug* and .pdr

They were included in the check for non-allocatable section
and caused modpost to warn.

Manuel Lauss suggested to fix this by adding the relevant
sections to the list of sections we do not check.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Reported-by: Manuel Lauss <mano@roarinelk.homelinux.net>