rtc: pcf2127: clear minute/second interrupt

rtc: pcf2127: clear minute/second interrupt

PCF2127 can generate interrupt every full second or minute configured
from control and status register 1, bits MI (1) and SI (0).

On interrupt control register 2 bit MSF (7) is set and must be cleared
to continue normal operation.

While the driver never enables this interrupt on its own, users or
firmware may do so - e.g. as an easy way to test the interrupt.

Add preprocessor definition for MSF bit and include it in the irq
bitmask to ensure minute and second interrupts are cleared when fired.

This fixes an issue where the rtc enters a test mode and becomes
unresponsive after a second interrupt has fired and is not cleared in
time. In this state register writes to control registers have no
effect and the interrupt line is kept asserted [1]:

[1] userspace commands to put rtc into unresponsive state:
$ i2cget -f -y 2 0x51 0x00
0x04
$ i2cset -f -y 2 0x51 0x00 0x05 # set bit 0 SI
$ i2cget -f -y 2 0x51 0x00
0x84 # bit 8 EXT_TEST set
$ i2cset -f -y 2 0x51 0x00 0x05 # try overwrite control register
$ i2cget -f -y 2 0x51 0x00
0x84 # no change

Signed-off-by: Josua Mayer <josua@solid-run.com>
Reviewed-by: Bruno Thomsen <bruno.thomsen@gmail.com>
Link: https://lore.kernel.org/r/20250825-rtc-irq-v1-1-0133319406a7@solid-run.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>