Input: tsc2007 - reduce I2C transactions for Z2 read

Input: tsc2007 - reduce I2C transactions for Z2 read

The current implementation sends a separate power-down command
after reading the Z2 value, resulting in an extra I2C
transaction per measurement cycle.

The TSC2007 command byte contains a 2-bit power-down mode
selection field. By selecting the power-down state in the Z2
measurement command, the device powers down after the Z2 A/D
conversion completes, eliminating the subsequent power-down
transaction.

This reduces the number of I2C transactions by one per touch
measurement cycle, decreasing I2C bus overhead and improving
touch sampling performance.

Signed-off-by: Yuki Horii <yuuki198708@gmail.com>
Tested-by: Andreas Kemnade <andreas@kemnade.info> # GTA04
Link: https://patch.msgid.link/20260410074100.1660-1-horiiyuk@ishida.co.jp
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>