x86/pat: Fix W=1 build warning when the within_inclusive() function is unused

The within_inclusive() function, in some cases, when CONFIG_X86_64=n,
may be not used.

This, in particular, prevents kernel builds with Clang, `make W=1`
and CONFIG_WERROR=y:

  arch/x86/mm/pat/set_memory.c:215:1: error: unused function 'within_inclusive' [-Werror,-Wunused-function]

Fix this by guarding the definitions with the respective ifdeffery.

See also:

  6863f564 ("kbuild: allow Clang to find unused static inline functions for W=1 build")

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20250211145721.1620552-1-andriy.shevchenko@linux.intel.com