mm: optimize thread stack usage on arm64 [1/1]

mm: optimize thread stack usage on arm64 [1/1]

PD#SWPL-1219

Problem:
On arm64, thread stack is 16KB for each task. If running task number
is large, this type of memory may over 40MB. It's a large amount on
small memory platform. But most case thread only use less 4KB stack.
It's waste of memory and we need optimize it.

Solution:
1. Pre-allocate a vmalloc address space for task stack;
2. Only map 1st page for stack and handle page fault in EL1
   when stack growth triggered exception;
3. handle stack switch for exception.

Verify:
p212

Change-Id: I47f511ccfa2868d982bc10a820ed6435b6d52ba9
Signed-off-by: tao zeng <tao.zeng@amlogic.com>