ciaa: Remove NOR flash-related configuration

The CIAA NXP LPC4337 has no NOR or CFI flash, so nuke all the flash config.
The SPIFI flash is MMIO, and can be treated as normal memory (plain read/write).

Signed-off-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
ciaa: Cleanup the default environment

Just some environment cleanup. Relevant changes include:

  * drop the clk_ignore_unused (problematic clock identified
    in the kernel and disable is prevented).
  * make the flashboot the default bootcmdº

Signed-off-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
ciaa: Add a macro to select between USART2 and USART3 console output

This commit adds a couple macros CIAA_CONSOLE_ON_USART2 and
CIAA_CONSOLE_ON_USART3 so we can easily switch between the two
available UARTs.

For quick development is really more useful to use USART3 (being
host-powered), but it means getting another cable, so I'm guessing
most people will rather just plug the board and connect to it through
the same cable. Therefore, the default is USART2 for now.

Signed-off-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>