b43: add IPA TX gain table for N-PHY r8 + radio 2057 r8

b43: add IPA TX gain table for N-PHY r8 + radio 2057 r8

Add the 2.4 GHz IPA TX gain table for N-PHY rev 8 paired with radio
2057 rev 8 and wire it to the existing dispatcher.

b43_nphy_get_ipa_gain_table() in tables_nphy.c currently handles
case 8 only for radio_rev == 5; radio_rev == 8 falls through and
the function logs:

    b43-phyX ERROR: No 2GHz IPA gain table available for this device
    b43-phyX ERROR: PHY init: Channel switch to default failed

leaving b43_phy_init() to return an error and core_init to abort
before the MAC is enabled.

The high byte of every entry differs from the rev 5 sibling (0x40
vs 0x30): different PAD-gain code prefix for the rev 8 front-end.
The low 24 bits coincide with rev 5 across the whole table - the
gain step amplitudes are the same, only the PAD-gain selector
prefix changes.

Values extracted from an MMIO dump of the proprietary Broadcom wl
driver running on BCM6362 silicon (wl driver 6.30.102.7).

Assisted-by: Claude:claude-4.7-opus
Signed-off-by: Alessio Ferri <alessio.ferri@mythread.it>
Acked-by: Michael Büsch <m@bues.ch>
Reviewed-by: Joshua Peisach <jpeisach@ubuntu.com>
Link: https://patch.msgid.link/20260528-b43_complete_n_phy_rev_8_radio_2057_rev_8_support-v4-5-464566194d47@gmail.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>