scripts/faddr2line: Check only two symbols when calculating symbol size

Rather than looping through each symbol in a particular section to
calculate a symbol's size, grep for the symbol and its immediate
successor, and only use those two symbols.

Signed-off-by: Brian Johannesmeyer <bjohannesmeyer@gmail.com>
Link: https://lore.kernel.org/r/20240415145538.1938745-8-bjohannesmeyer@gmail.com


Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>