mips: switch to generic sys_fork() and sys_clone()

we still need the wrappers to store callee-saved registers in
pt_regs, but once that done we can jump to kernel/fork.c variants.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 7352acf..0772b5c 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -41,6 +41,7 @@
 	select HAVE_MOD_ARCH_SPECIFIC
 	select MODULES_USE_ELF_REL if MODULES
 	select MODULES_USE_ELF_RELA if MODULES && 64BIT
+	select CLONE_BACKWARDS
 	select GENERIC_SIGALTSTACK
 	select GENERIC_COMPAT_RT_SIGACTION
 	select GENERIC_COMPAT_RT_SIGQUEUEINFO