net: mvpp2: cls: Write C2 TCAM data last when writing a C2 entry

When writing a C2 entry to hardware, some registers writes will only
take effect when the TCAM_DATA4 register is written. This includes all
C2 TCAM registers, and the C2 invalidate register.

To make sure we always write C2 entries correctly, document that
behaviour with a comment, and move TCAM writes to the end of the
mvpp2_cls_c2_write helper.

Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>