arch/mips: Add basic support for MIPS Creator CI20 board

This commit introduces a rudimentary architecture and board port for the
MIPS Creator CI20, featuring the dual core Ingenic JZ4780 SoC (MIPS32).

Included in this initial implementation:
- Basic architectural initialization and startup code for the JZ4780 Core 0.
- Minimal configuration required to execute from RAM.
- Early UART/serial console support for basic debugging and NSH output.
- Minimal board-specific configuration for the CI20 target.
- Console output is routed via UART0 on the expansion header.

This establishes basic support for running NuttX on the MIPS CI20.
Further peripherals, optimization, and extended documentation are left for
future iterations or community contributions.

Build and Runtime Deployment Info:
----------------------------------

The baseline can be configured, compiled using the MIPS MTI toolchain,
and loaded via U-Boot using the following commands (replace
<tftp_dir> with your local TFTP root directory).

./tools/configure.sh -l ci20/nsh
  make CROSSDEV=mips-mti-elf-
  mkimage -A mips -O linux -T kernel -C none -a 0x80000180 -e 0x800004ac \
    -n "nx" -d nuttx.bin <tftp_dir>/nuttx.umg

Note: U-Boot must be properly configured for networking (e.g., valid ipaddr,
serverip, and ethaddr environment variables) to fetch the image over TFTP.

Run this from U-Boot prompt:
  tftp nuttx.umg && bootm $fileaddr

Signed-off-by: Lwazi Dube <lwazeh@gmail.com>

drivers/serial/uart_16550.c

@@ -1583,7 +1583,8 @@ static void u16550_send(struct uart_dev_s *dev, int ch)
 static ssize_t u16550_sendbuf(struct uart_dev_s *dev,
                               const void *buffer, size_t size)
 {
-  for (size_t i = 0; i < size; i++)
+  size_t i;
+  for (i = 0; i < size; i++)
     {
       while (!u16550_txready(dev));
       u16550_send(dev, ((const unsigned char *)buffer)[i]);