[PATCH] include: update jiffies/{m,u}secs conversion functions

Clarify the human-time units to jiffies conversion functions by using the
constants in time.h.  This makes many of the subsequent patches direct
copies of the current code.

Signed-off-by: Nishanth Aravamudan <nacc@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>