lib/cmdline.c: add size unit t/p/e to memparse

lib/cmdline.c: add size unit t/p/e to memparse

For modern filesystems such as btrfs, t/p/e size level operations are
common.  add size unit t/p/e parsing to memparse

Signed-off-by: Gui Hecheng <[email protected]>
Acked-by: David Rientjes <[email protected]>
Reviewed-by: Satoru Takeuchi <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>