Add unit-aware cylinder size string parserc

Whittling down on the string parsing that doesn't check user-specified
units.  Still need to handle temperatures (and will do percentages to
match the pattern too), but this is getting us closer to always honoring
user-specified units.

With this you can say that you have a "10l" cylinder at "3000psi", and
it will do the right thing (it's basically a 72 cuft cylinder in
imperial measurements).

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Add and use 'string_to_fraction()' helper converter function

This matches the pattern of unit conversion, and will allow us to remove
all the code that uses the old complex "CHANGED()" macro that tries to
remove units or percent signs.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Remove now stale arguments to "CHANGED()" macro

We now never remove units or percentage signs, and always just compare
the string data, so we should remove the hacky arguments that are no
longer used.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>