kbuild: whitelist references from __dbe_table to .init

This is needed on MIPS where the same mechanism as get_user() is used to
intercept bus error exceptions for some hardware probes.  Without this
patch modpost will throw spurious warnings:

  LD      vmlinux
  SYSMAP  System.map
  SYSMAP  .tmp_System.map
  MODPOST vmlinux
WARNING: arch/mips/sgi-ip22/built-in.o(__dbe_table+0x0): Section mismatch: reference to .init.text:

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Cc: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>