drm/xe/ct: Separate waiting for retry from ct send function

drm/xe/ct: Separate waiting for retry from ct send function

The function `guc_ct_send_locked()` is really quite simple, but still
looks complex due to exposed internals. It is sending a message,
and in case of lack of space, waiting for a proper moment to send
a retry.

Clear separation of send function and wait function will help with
readability. This is a cosmetic change only, no functional difference
is expected.

This patch introduces `guc_ct_send_wait_for_retry()`, and uses it to
greatly simplify `guc_ct_send_locked()`.

Signed-off-by: Tomasz Lis <tomasz.lis@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Link: https://lore.kernel.org/r/20251009170844.178199-1-tomasz.lis@intel.com