drm/gpusvm: Drop redundant @flags.* kernel-doc on struct drm_gpusvm_pages

drm/gpusvm: Drop redundant @flags.* kernel-doc on struct drm_gpusvm_pages

The kernel-doc block above struct drm_gpusvm_pages duplicates the
descriptions of the bit-flags that live in struct drm_gpusvm_pages_flags
using dotted notation (@flags.migrate_devmem, @flags.unmapped, ...).
That dotted notation is intended for nested anonymous structs/unions that
the parser flattens into the parent's parameter list.  Here, however,
flags is of a named external type, so the parser does not flatten its
members and the dotted entries do not match any member of
drm_gpusvm_pages.  They also duplicate the canonical descriptions already
present in the kernel-doc of struct drm_gpusvm_pages_flags itself.

Drop the five @flags.* lines and replace them with a single @flags entry
that cross-references the type via kernel-doc's "&struct ..." syntax.
This eliminates the redundancy and removes warnings emitted by the new
parameterdescs check in scripts/kernel-doc:

  Excess struct member 'flags.migrate_devmem' description in
   'drm_gpusvm_pages'
  Excess struct member 'flags.unmapped' description in 'drm_gpusvm_pages'
  Excess struct member 'flags.partial_unmap' description in
   'drm_gpusvm_pages'
  Excess struct member 'flags.has_devmem_pages' description in
   'drm_gpusvm_pages'
  Excess struct member 'flags.has_dma_mapping' description in
   'drm_gpusvm_pages'

No functional change.

Assisted-by: Claude:claude-opus-4.6
Cc: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Shuicheng Lin <shuicheng.lin@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patch.msgid.link/20260501175956.4054088-1-shuicheng.lin@intel.com