uapi: add INT_MAX and INT_MIN constants

uapi: add INT_MAX and INT_MIN constants

Some UAPI headers use INT_MAX and INT_MIN. Currently they include
<limits.h> for their definitions, which introduces a problematic
dependency on libc.

Add custom, namespaced definitions of INT_MAX and INT_MIN using the
same values as the regular kernel code.
These definitions are not added to uapi/linux/limits.h, as that header
will conflict with libc definitions on some platforms.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Link: https://patch.msgid.link/20260113-uapi-limits-v2-1-93c20f4b2c1a@linutronix.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>