objtool: Increase per-function WARN_FUNC() rate limit

Increase the per-function WARN_FUNC() rate limit from 1 to 2.  If the
number of warnings for a given function goes beyond 2, print "skipping
duplicate warning(s)".  This helps root out additional warnings in a
function that might be hiding behind the first one.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/aec318d66c037a51c9f376d6fb0e8ff32812a037.1741975349.git.jpoimboe@kernel.org