MIPS: Remove "__weak" definition from arch-specific linkage.h

MIPS: Remove "__weak" definition from arch-specific linkage.h

"__weak" is defined in include/linux/compiler-gcc.h.  We shouldn't need an
arch-specific definition.

Remove the "__weak" definition from arch/mips/include/asm/linkage.h.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: James Hogan <james.hogan@imgtec.com>
Cc: Andrew Bresticker <abrestic@chromium.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/10689/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>