cpu_func.h: provide noncached_set_region prototype to fix build

cpu_func.h: provide noncached_set_region prototype to fix build

Due to the removal of weak functions in 7d6cee2cd0 ("cmd: cache: Remove
weak function"), U-Boot fails to compile after updating to v2024.10 for
mediatek target in OpenWrt with GCC-14 with error:
cmd/cache.c: In function 'do_dcache':
cmd/cache.c:57:25: error: implicit declaration of function
	'noncached_set_region' [-Wimplicit-function-declaration]

Thus, provide a prototype in include/cpu_func.h to fix a build
error in cmd/cache.c, since related prototypes are also located there.

The issue occurred after the update of uboot-mediatek in OpenWrt to
v2024.10, in combination with GCC-14 toolchain. It was reported and
discussed in https://github.com/openwrt/openwrt/issues/16697, and
temporarily fixed with
https://github.com/openwrt/openwrt/commit/92ca322dd1f48158b8829fec59319a12e4ae4295.

Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>
Link: https://github.com/openwrt/openwrt/issues/16697
Link: https://github.com/openwrt/openwrt/commit/92ca322dd1f48158b8829fec59319a12e4ae4295
Fixes: 7d6cee2cd0 ("cmd: cache: Remove weak function")
Signed-off-by: Tom Rini <trini@konsulko.com>