soc: ti: wkup_m3_ipc: Document 'm3_ipc' parameter throughout

Fixes the following W=1 kernel build warning(s):

 drivers/soc/ti/wkup_m3_ipc.c:227: warning: Function parameter or member 'm3_ipc' not described in 'wkup_m3_set_mem_type'
 drivers/soc/ti/wkup_m3_ipc.c:236: warning: Function parameter or member 'm3_ipc' not described in 'wkup_m3_set_resume_address'
 drivers/soc/ti/wkup_m3_ipc.c:248: warning: Function parameter or member 'm3_ipc' not described in 'wkup_m3_request_pm_status'
 drivers/soc/ti/wkup_m3_ipc.c:268: warning: Function parameter or member 'm3_ipc' not described in 'wkup_m3_prepare_low_power'
 drivers/soc/ti/wkup_m3_ipc.c:322: warning: Function parameter or member 'm3_ipc' not described in 'wkup_m3_finish_low_power'
 drivers/soc/ti/wkup_m3_ipc.c:369: warning: Function parameter or member 'm3_ipc' not described in 'wkup_m3_set_rtc_only'
 drivers/soc/ti/wkup_m3_ipc.c:369: warning: Excess function parameter 'wkup_m3_wakeup' description in 'wkup_m3_set_rtc_only'

Cc: Santosh Shilimkar <ssantosh@kernel.org>
Cc: Dave Gerlach <d-gerlach@ti.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>