SPI: chip select can now be kept active if the bus has been acquired

The user can now request the chip select to remain active after the current
transfer. In order to do so, he MUST acquire the bus first with `spi_device_acquire_bus()`
function, else, an error is returned.

components/hal/spi_hal_iram.c

@@ -131,6 +131,9 @@ void spi_hal_setup_trans(spi_hal_context_t *hal, const spi_hal_dev_config_t *dev
     spi_ll_set_command(hw, trans->cmd, cmdlen, dev->tx_lsbfirst);
     spi_ll_set_address(hw, trans->addr, addrlen, dev->tx_lsbfirst);
 
+    //Configure keep active CS
+    spi_ll_master_keep_cs(hw, trans->cs_keep_active);
+
     //Save the transaction attributes for internal usage.
     memcpy(&hal->trans_config, trans, sizeof(spi_hal_trans_config_t));
 }