driver/sensors: lis2dh: Fix I2C and SPI bus communication

Add I2C and SPI bus communication routines in separate files,
and register one or the other as read/write callbacks based
on bus selection in DTS.

This commit is fixing issue #22348 as well, as the SPI part
is handling in the proper way the CS GPIO part.

Signed-off-by: Armando Visconti <armando.visconti@st.com>