i2c: designware: size the RX FIFO threshold to the queued transfer

i2c_dw_xfer_msg() leaves DW_IC_RX_TL at the 0 that i2c_dw_configure_mode()
writes, so the controller raises RX_FULL once per received byte. Program
RX_TL from the reads already queued, capped at half the FIFO until the last
message is queued, so there is room for the rest.

On an Arrow Lake-H LPSS core with rx_fifo_depth 32, a 22-byte HID input
report costs 2.00 interrupts instead of 21.43, and a 452-byte descriptor
0.14 interrupts per byte instead of 1.64. Polling the touchpad with
HIDIOCGINPUT at 142 Hz draws 1.58 W less platform power (psys, 32 paired
runs).

Assisted-by: LLM
Signed-off-by: Navon John Lukose <navonjohnlukose@gmail.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
Link: https://patch.msgid.link/20261007191911.502428-1-navonjohnlukose@gmail.com

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