drivers: i2c: i2c_dw: only includ cmsis_core on ARM platforms

Only include cmsis_core.h on ARM platforms, including it unconditionally
as it is now causes a build failure on all other platforms, namely x86
on the weekly build run.

Tested with:

west build -p -b up_squared/apollo_lake tests/drivers/build_all/led
(and others)

Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>