realtek: mark clock source as continuous

realtek: mark clock source as continuous

After replacing the R4K event timer and clock source with the new
Realtek Otto timer, performance for RTL839x devices was severely
impacted, as reported by Hiroshi.

Research by Markus showed that after commit 4657a5301eb5 ("realtek:
avoid busy waiting for RTL839x PHY read/write"), the ethernet driver
could only update a phy once per timer interval, which also heavily
impacted boot time. On e.g. a Zyxel GS1900-48, this added around a
minute to the time to fully initialise the switch.

By marking the otto clocksource as continuous, the kernel enables it to
be used for high resolution timers. This allows readx_poll_timeout() to
sleep for less than one system timer interval, reducing system dead
time.

Link: https://github.com/openwrt/openwrt/issues/11117
Reported-by: INAGAKI Hiroshi <musashino.open@gmail.com>
Cc: Markus Stockhausen <markus.stockhausen@gmx.de>
Signed-off-by: Sander Vanheule <sander@svanheule.net>
Tested-by: INAGAKI Hiroshi <musashino.open@gmail.com> # Panasonic Switch-M48eG PN28480K
Tested-by: Jan Hoffmann <jan@3e8.eu> # HPE 1920-8G, HPE 1920-48G