rtc: m41t93: Add square wave clock provider support

rtc: m41t93: Add square wave clock provider support

Implement support to configure square wave output (SQW) of m41t93 rtc
via common clock framework clock provider api. Add clock provider
callbacks to control output frequency ranging from 1Hz to 32KHz as
supported by this rtc chip.

Use clock framework debugfs interface or clock consumer DT node to test.
Tested by measuring various frequencies on pull-up connected SWQ(7) pin
of m41t93 rtc chip using logic analyzer.

Signed-off-by: Akhilesh Patil <akhilesh@ee.iitb.ac.in>
Link: https://patch.msgid.link/a8c4d3741be4e9dfa52c57cbd653f561ba4ed934.1758379856.git.akhilesh@ee.iitb.ac.in
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>