spi/sh-hspi: add CS manual control support

The current HSPI driver used automatic CS control, leading to CS
active for each byte transmitted. This patch changes the driver
to manual CS control, and ensures CS is active thoughout a whole
message. Additionally, it uses the cs_change field to determine
if CS is disabled between transfers in the message.

Signed-off-by: Phil Edworthy <phil.edworthy@renesas.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>