drm/tegra: tegra_drm.h: fix all uapi kernel-doc warnings

drm/tegra: tegra_drm.h: fix all uapi kernel-doc warnings

Add 2 struct member descriptions and convert #define macro constants
comments to kernel-doc comments to eliminate all kernel-doc warnings:

Warning: include/uapi/drm/tegra_drm.h:353 struct member 'cmdbuf' not
 described in 'drm_tegra_reloc'
Warning: include/uapi/drm/tegra_drm.h:353 struct member 'target' not
 described in 'drm_tegra_reloc'

Warning: include/uapi/drm/tegra_drm.h:780 This comment starts with '/**',
 but isn't a kernel-doc comment.
 * Specify that bit 39 of the patched-in address should be set to switch
Warning: include/uapi/drm/tegra_drm.h:832 This comment starts with '/**',
 but isn't a kernel-doc comment.
 * Execute `words` words of Host1x opcodes specified in the
 `gather_data_ptr`
Warning: include/uapi/drm/tegra_drm.h:837 This comment starts with '/**',
 but isn't a kernel-doc comment.
 * Wait for a syncpoint to reach a value before continuing with further
Warning: include/uapi/drm/tegra_drm.h:842 This comment starts with '/**',
 but isn't a kernel-doc comment.
 * Wait for a syncpoint to reach a value before continuing with further

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Mikko Perttunen <mperttunen@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patch.msgid.link/20260427184454.693794-1-rdunlap@infradead.org