rtc: optee: add alarm related rtc ops to optee rtc driver

Add read_alarm and set_alarm ops from the rtc framework.
The support of an alarm is handled by a kernel thread waiting in OP-TEE
for an asynchronous notification that comes in the interrupt
handler of the alarm interruption on OP-TEE secure world.

Once the notification arrives, the kernel thread previously suspended
is rescheduled (this is handled by the OP-TEE kernel driver) and comes
back with the alarm information to the kernel.

A second session is therefore needed to enable/disable/cancel a waiting
alarm event as the kernel thread stopped in OP-TEE takes a form of mutex
on the session and so no one can use this session in parallel.

Signed-off-by: Clément Le Goffic <clement.legoffic@foss.st.com>
Link: https://lore.kernel.org/r/20250715-upstream-optee-rtc-v1-3-e0fdf8aae545@foss.st.com


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>