[CORE] vmm_devtree: Add vmm_devtree_next_u32() API

This patch adds vmm_devtree_next_u32() API and related linux-compatible
APIs in linux/of.h for driver porting.

Signed-off-by: Anup Patel <anup@brainfault.org>
[CORE] Add VMM_ESHUTDOWN error code.

This patch adds VMM_ESHUTDOWN error code to vmm_error.h and
ESHUTDOWN in asm/errno.h for driver porting.

Signed-off-by: Anup Patel <anup@brainfault.org>
[DRIVERS] Linux compatible linux/notifier.h for driver porting

We already have linux-like notifier APIs in vmm_notifier.h hence
this patch provides linux-compatible notifier APIs in linux/notifier.h.

Signed-off-by: Anup Patel <anup@brainfault.org>
[DRIVERS] More improvements to linux-compatiblity headers

This patch does misc updates to linux/clk.h, linux/init.h,
linux/kthread.h, linux/sched.h, linux/slab.h, and linux/spinlock.h.

Signed-off-by: Anup Patel <anup@brainfault.org>
[DRIVERS] clk: Make common clocking framework very close to linux

This patch makes our ported common clocking framework very close to
linux-3.15 with minimum possible diff so that it is easy to keep common
clocking framework in-sync with linux source.

Signed-off-by: Anup Patel <anup@brainfault.org>