objtool: Make struct entries[] static and const

This data is not modified and not used outside of special.c.

Also adapt its users to the constness.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Link: https://lore.kernel.org/r/20221216-objtool-memory-v2-1-17968f85a464@weissschuh.net


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