drm/xe/uapi: Fix kernel-doc cross-reference syntax in xe_drm.h

drm/xe/uapi: Fix kernel-doc cross-reference syntax in xe_drm.h

Fix incorrect kernel-doc cross-reference markup syntax
throughout xe_drm.h:
- @struct_name -> &struct name for cross-references to other
  structs (19 occurrences)
- struct @name -> &struct name where struct keyword was
  mixed with @ syntax (8 occurrences)
- enum @name -> &enum name for cross-references to other
  enums (5 occurrences)
- &CONSTANT / @CONSTANT -> %CONSTANT for defines and enum
  values (15 occurrences)
- @field references to members of other structs -> plain text,
  since @ only applies to the current struct's members
  (9 occurrences)

Per kernel-doc conventions (Documentation/doc-guide/kernel-doc.rst):
- '&struct name' creates hyperlinks to struct definitions
- '&enum name' creates hyperlinks to enum definitions
- '%NAME' references constants and defines
- '@name' is only for parameters/members of the current context

Assisted-by: GitHub Copilot:claude-opus-4.6
Suggested-by: Xin Wang <x.wang@intel.com>
Reviewed-by: Xin Wang <x.wang@intel.com>
Link: https://patch.msgid.link/20260407030046.3394004-5-shuicheng.lin@intel.com
Signed-off-by: Shuicheng Lin <shuicheng.lin@intel.com>