iommupt: Make pt_feature() always_inline

iommupt: Make pt_feature() always_inline

gcc 8.5 on powerpc does not automatically inline these functions even
though they evaluate to constants in key cases. Since the constant
propagation is essential for some code elimination and built-time checks
this causes a build failure:

 ERROR: modpost: "__pt_no_sw_bit" [drivers/iommu/generic_pt/fmt/iommu_amdv1.ko] undefined!

Caused by this:

	if (pts_feature(&pts, PT_FEAT_DMA_INCOHERENT) &&
	    !pt_test_sw_bit_acquire(&pts,
				    SW_BIT_CACHE_FLUSH_DONE))
		flush_writes_item(&pts);

Where pts_feature() evaluates to a constant false. Mark them as
__always_inline to force it to evaluate to a constant and trigger the code
elimination.

Fixes: 7c5b184db714 ("genpt: Generic Page Table base API")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202512230720.9y9DtWIo-lkp@intel.com/
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>