drm/i915: fix build error some more

An earlier patch fixed a build failure with clang, but I still see the
same problem with some configurations using gcc:

drivers/gpu/drm/i915/i915_pmu.c: In function 'config_mask':
include/linux/compiler_types.h:568:38: error: call to '__compiletime_assert_462' declared with attribute error: BUILD_BUG_ON failed: bit > BITS_PER_TYPE(typeof_member(struct i915_pmu, enable)) - 1
drivers/gpu/drm/i915/i915_pmu.c:116:3: note: in expansion of macro 'BUILD_BUG_ON'
116 | BUILD_BUG_ON(bit >

As I understand it, the problem is that the function is not always fully
inlined, but the __builtin_constant_p() can still evaluate the argument
as being constant.

Marking it as __always_inline so far works for me in all configurations.

Fixes: 686d773186bf ("drm/i915/pmu: Fix build error with GCOV and AutoFDO enabled")
Fixes: a644fde77ff7 ("drm/i915/pmu: Change bitmask of enabled events to u32")
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20250620111824.3395007-1-arnd@kernel.org
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>