ITE soc/it8xxx2/linker: add sections for hw sha256 calculation

IT8XXX2 HW support sha256 calculation, and its calculation is
faster than FW. We place SHA256 message, hash and key data
(total 512bytes) in RAM. If we enable hw sha256, because
HW limits, the sha256 data must place in first 4KB of RAM.
We add sections for hw sha256 calculation in linker.

Signed-off-by: Dino Li <Dino.Li@ite.com.tw>
Signed-off-by: Ruibin Chang <Ruibin.Chang@ite.com.tw>