Detach sched.h from mm.h

First thing mm.h does is including sched.h solely for can_do_mlock() inline
function which has "current" dereference inside. By dealing with can_do_mlock()
mm.h can be detached from sched.h which is good. See below, why.

This patch
a) removes unconditional inclusion of sched.h from mm.h
b) makes can_do_mlock() normal function in mm/mlock.c
c) exports can_do_mlock() to not break compilation
d) adds sched.h inclusions back to files that were getting it indirectly.
e) adds less bloated headers to some files (asm/signal.h, jiffies.h) that were
   getting them indirectly

Net result is:
a) mm.h users would get less code to open, read, preprocess, parse, ... if
   they don't need sched.h
b) sched.h stops being dependency for significant number of files:
   on x86_64 allmodconfig touching sched.h results in recompile of 4083 files,
   after patch it's only 3744 (-8.3%).

Cross-compile tested on

	all arm defconfigs, all mips defconfigs, all powerpc defconfigs,
	alpha alpha-up
	arm
	i386 i386-up i386-defconfig i386-allnoconfig
	ia64 ia64-up
	m68k
	mips
	parisc parisc-up
	powerpc powerpc-up
	s390 s390-up
	sparc sparc-up
	sparc64 sparc64-up
	um-x86_64
	x86_64 x86_64-up x86_64-defconfig x86_64-allnoconfig

as well as my two usual configs.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 2 insertions, 0 deletions

diff --git a/arch/x86_64/ia32/mmap32.c b/arch/x86_64/ia32/mmap32.c
index 079f4132575c..e4b84b4a417a 100644
--- a/arch/x86_64/ia32/mmap32.c
+++ b/arch/x86_64/ia32/mmap32.c
@@ -29,6 +29,7 @@
 #include <linux/personality.h>
 #include <linux/mm.h>
 #include <linux/random.h>
+#include <linux/sched.h>
 
 /*
  * Top of mmap area (just below the process stack).
diff --git a/arch/x86_64/kernel/reboot.c b/arch/x86_64/kernel/reboot.c
index c116b54d422e..7503068e788d 100644
--- a/arch/x86_64/kernel/reboot.c
+++ b/arch/x86_64/kernel/reboot.c
@@ -8,6 +8,7 @@
 #include <linux/string.h>
 #include <linux/pm.h>
 #include <linux/kdebug.h>
+#include <linux/sched.h>
 #include <asm/io.h>
 #include <asm/delay.h>
 #include <asm/hw_irq.h>