drivers: i2s: mcux_flexcomm: fix multiple bugs

Fix for bugs described in:
https://github.com/zephyrproject-rtos/zephyr/issues/59803



1. the size argument passed to i2s_write() was being ignored.
   change the code so that the size is queued with the
   tx mem_block and the dma transfer is configured with this
   size.

2. change how CONFIG_I2S_MCUX_FLEXCOMM_RX_BLOCK_COUNT and
   CONFIG_I2S_MCUX_FLEXCOMM_TX_BLOCK_COUNT are used so that
   the queue buffers are allocated correctly when the two
   config values are not the same

3. set source_data_size and dest_data_size to be the same
   since the DMA controller can only set one size per
   DMA transfer. the driver was already computing a dest_data_size
   but always passing 1 for the source_data_size.
   For I2S RX case, I think source_data_size should be
   set to the expected FIFO read size instead of dest_data_size.

Also some smaller improvements like:
* don't allocate two dma_blocks for tx in the static dev_mem
  when it only needs one
* memset both rx_dma_blocks together instead of separtely
* set dma_cfg block_count for tx and rx statically instead
  of at runtime

Signed-off-by: Mike J. Chen <mjchen@google.com>