seq_file: Allocate memory using vmalloc when kmalloc failed

When dumpstate access /proc/xxx/binder, this binder include lots of info,
it will use seq_read in kernel, in this function, it will trigger
high order memory alloc, when read binder info or other large file,
this will cause memory presure when system don't have contious high order
memory, it will lead to high kswap workload to reclaim the page. so change
kmalloc to vmalloc, it can avoid contiously high order memory allocating.

CRs-fixed: 514982

Change-Id: I463d5f72c24b7bb298e14b0da49c5fc96091ecc1
Patch-mainline: linux-arm-kernel(lkml) @ Thu, 31 Jan 2013 14:11:32 +0800
Link : https://lkml.org/lkml/2013/1/31/20


Signed-off-by: Srinivasarao P <spathi@codeaurora.org>