Allow redirection of console output prior to console initialisation to a
temporary buffer.
To enable this functionality, the board (or arch) must define:
- CONFIG_PRE_CONSOLE_BUFFER - Enable pre-console buffer
- CONFIG_PRE_CON_BUF_ADDR - Base address of pre-console buffer
- CONFIG_PRE_CON_BUF_SZ - Size of pre-console buffer (in bytes)
The pre-console buffer will buffer the last CONFIG_PRE_CON_BUF_SZ bytes
Any earlier characters are silently dropped.
