it83xx/flash: exclude immu tag workaround if chip's core is riscv
it83xx/flash: exclude immu tag workaround if chip's core is riscv

This issue is present on chip with N8 core only. So we don't
need to apply the workaround for chip with RISCV core to save
time of writing and erasing.

BUG=none
BRANCH=none
TEST=use console "flasherase" and "flashwrite" commands to erase/write
these two 4KB blocks(0x7e000 ~ 0x7ffff) on both IT8320 and IT81202,
no error message occurred.

Signed-off-by: Dino Li <338d523ecf3700bd86eb9c34d220f91911d2a18c@ite.com.tw>
Change-Id: I9aeb7e32048dafb2fa54bf1a137ecafb5a854b91
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2109438
Reviewed-by: Jett Rink <9d4aef0593e6843318d99df31597fb6153b89787@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec