net: dsa: microchip: Wrap timestamp reading in a function

net: dsa: microchip: Wrap timestamp reading in a function

Timestamps are directly accessed through a register read in the
interrupt handler. KSZ8463's logic to access it will be a bit more
complex because the same interrupt can be triggered by two different
timestamps being ready.

Wrap the timestamp's reading in a dedicated function to ease the
KSZ8463's integration in upcoming patches.

Signed-off-by: Bastien Curutchet (Schneider Electric) <bastien.curutchet@bootlin.com>
Link: https://patch.msgid.link/20260105-ksz-rework-v1-9-a68df7f57375@bootlin.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>