Remove duplicated definition of THREAD_SIZE, it is defined in page.h.
Also modify asm constraints to explicilty let gas know that the input
arg is a constant in the current_thread_info() function.

Patch originally submitted by Philippe De Muyter <phdm@macqel.be>
Signed-off-by: Greg Ungerer <gerg@snapgear.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>