tracing: fix undeclared 'PAGE_SIZE' in include/linux/trace_seq.h

when compiling linux-mips with kmemtrace enabled, there will be an
error:

include/linux/trace_seq.h:12: error: 'PAGE_SIZE' undeclared here (not in
				a function)

I checked the source code and found trace_seq.h used PAGE_SIZE but not
included the relative header file, so, fix it via adding the header file
<asm/page.h>

Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Wu Zhangjin <wuzj@lemote.com>
LKML-Reference: <1244962350-28702-1-git-send-email-wuzhangjin@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>