drm: clean up unused kerneldoc in drm_lease.c

The kerneldoc in drm_lease.c is unused because none of the functions
are driver interfaces as the symbols are not exported.

Since they aren't used and much of the existing comments don't provide
any insights (e.g. they just repeat the function name or list out the
function parameters), they should be removed to make them easier to
maintain and to make useful info more obvious.

As a note, many of the comments mention whether idr_mutex should be
held, but these are mostly redundant in cases where the function
contains lockdep assertions or grabs the mutex.

To simplify review, here's the reasoning behind each update.

drm_lease_owner:
function name is self-descriptive

_drm_find_lessee:
function name is self-descriptive

_drm_lease_held_master:
function name and signature are self-descriptive

_drm_has_leased:
kerneldoc is summarized into a comment because the function name could
be interpreted ambiguously (check if the object has been leased VS
check if the master has a lease on the object)

_drm_lease_held:
Retain the idr_mutex comment because the function does not directly
grab the mutex or use a lockdep assertion.
Otherwise, the function name is self-descriptive.

drm_lease_held:
function name is self-descriptive

drm_lease_filter_crtcs:
Kerneldoc is summarized into a comment because the function name could
be interpreted ambiguously (filter leases based on crtcs mask VS
filter crtcs mask based on leases)

drm_lease_create:
Kerneldoc removed.
Useful function details such as atomic leasing are retained.
Errno interpretations are useful and retained.

drm_lease_destroy:
function name is self-descriptive. Additional information is also
removed as they're already present as comments inside the function.

_drm_lease_revoke:
function name is self-descriptive

drm_lease_revoke:
function name is self-descriptive

drm_mode_create_lease_ioctl:
Kerneldoc removed, but useful function details retained.

drm_mode_list_lessees_ioctl:
function name is self-descriptive. Additional details restate what the
code does.

drm_mode_get_lease_ioctl:
Function summary retained to clarify that it's the leased objects that
are returned, not the lease structure.

drm_mode_revoke_lease_ioctl:
Kerneldoc removed, but useful function details retained.

Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210730051759.1570630-1-desmondcheongzx@gmail.com