kbuild: uapi: completely exclude linux/bpf_perf_event.h on nios2

kbuild: uapi: completely exclude linux/bpf_perf_event.h on nios2

This header is actually not buildable on nios. As nobody built nios2
with CONFIG_CC_CAN_LINK=y so far, this produced no errors.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Nicolas Schier <nsc@kernel.org>
Tested-by: Nicolas Schier <nsc@kernel.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Link: https://patch.msgid.link/20260227-kbuild-uapi-libc-v1-4-c17de0d19776@weissschuh.net
Signed-off-by: Nicolas Schier <nsc@kernel.org>