phy: lynx-28g: make lynx_28g_pll_read_configuration() callable per PLL

phy: lynx-28g: make lynx_28g_pll_read_configuration() callable per PLL

In a future change, lynx_28g_pll_read_configuration() and
lynx_28g_lane_read_configuration() will be made methods of struct
lynx_info.

There is no functional reason, but lynx_28g_lane_read_configuration() is
called per lane and lynx_28g_pll_read_configuration() iterates over PLLs
internally. So the API exported by the lynx_info structure would not be
uniform. Change lynx_28g_pll_read_configuration() to also permit reading
the PLL configuration individually, and move the for loop at the call
site.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://patch.msgid.link/20260610151952.2141019-10-vladimir.oltean@nxp.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>