net: stmmac: hw->ps becomes hw->reverse_sgmii_enable

net: stmmac: hw->ps becomes hw->reverse_sgmii_enable

After a lot of digging, it seems that the oddly named hw->ps member
is all about setting the core into reverse SGMII speed. When set to
a non-zero value, it:

1. Configures the MAC at initialisation time to operate at a specific
   speed.
2. It _incorrectly_ enables the transmitter (GMAC_CONFIG_TE) which
   makes no sense, rather than enabling the "transmit configuration"
   bit (GMAC_CONFIG_TC).
3. It configures the SGMII rate adapter layer to retrieve its speed
   setting from the MAC configuration register rather than the PHY.

In the previous commit, we removed (1) and (2) as phylink overwrites
the configuration set at that step.

Thus, the only functional aspect is (3), which is a boolean operation.
This means there is no need to store the actual speed, and just have a
boolean flag.

Convert the priv->ps member to a boolean, and rename it to
priv->reverse_sgmii_enable to make it more understandable.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Tested-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Tested-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Link: https://patch.msgid.link/E1v9P6i-0000000Aom3-1y2y@rmk-PC.armlinux.org.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>