spi: dw: Add update_cr0() callback to update CTRLR0

spi: dw: Add update_cr0() callback to update CTRLR0

This patch adds update_cr0() callback, in struct dw_spi.

Existing code that configure register CTRLR0 is moved into a new
function, dw_spi_update_cr0(), and this will be the default.

Suggested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Wan Ahmad Zainie <wan.ahmad.zainie.wan.mohamad@intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20200505130618.554-3-wan.ahmad.zainie.wan.mohamad@intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>