realtek: pcs: rtl93xx: share IP mode register write

realtek: pcs: rtl93xx: share IP mode register write

RTL930x and RTL931x program the same physical SerDes IP mode field
(page 0x1f reg 0x09, bits 11:7 hold the 5-bit mode value, bit 6 is
the "force mode" enable), but did so via two unrelated code paths:
RTL930x kept the force bit separate from the value in a __set helper,
while RTL931x had it baked into each switch-case constant.

Add a shared rtpcs_93xx_sds_set_ip_mode() that takes the rtpcs_sds_mode
enum, looks up the 5-bit value from the existing sds_hw_mode_vals
table, and writes value | force-bit in one place.

Convert both variants:
 - RTL930x: drop __rtpcs_930x_sds_set_ip_mode and the manual table
   lookup; __rtpcs_930x_sds_get_ip_mode is replaced by the shared
   rtpcs_93xx_sds_get_ip_mode, which reverse-looks the raw register
   value up in sds_hw_mode_vals[] and returns the matching enum
   rtpcs_sds_mode (or -ENOENT for an unmapped raw value). The
   wrapper that orchestrates power, CMU, state machine and rx-reset
   around the mode write is renamed to rtpcs_930x_sds_apply_ip_mode
   for clarity.
 - RTL931x: drop the per-mode switch and the leftover pr_info debug
   print; rename the symerr-clear + MAC-OFF + IP-mode-write wrapper
   to rtpcs_931x_sds_apply_ip_mode.

rtpcs_930x_sds_reconfigure_to_pll() now goes through the new shared
get/set helpers: it saves the current IP mode as an enum on entry
and restores it via the enum-taking setter after the PLL reconfigure.
This changes behavior by mapping the raw mode setting through the
hardware mode table, effectively blocking unknown modes which might be
set by bootloader or somewhere else. This is intended and might uncover
unknown behavior instead of hiding it.

As a side-effect, QSGMII is now properly set too for RTL931x. Most code
paths anyway already had support for this mode, but it was missing from
the mode setting.

Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/23213
Signed-off-by: Robert Marko <robimarko@gmail.com>