Update UART selection for Boot ROM ets_putc, when debug port is selected. (#6489)

* Add code to select the UART for Boot ROM ets_putc which is used by
::printf, ets_printf_P in core_esp_postmortem.cpp and others.

ets_putc is a wrapper for uart_tx_one_char. uart_tx_one_char uses
the element buff_uart_no in UartDev (A structure in data area of the
Boot ROM) to select UART0 or UART1. uart_buff_switch is used to set
that entry.

The structure for UartDev can be found in uart.h from the
ESP8266_NONOS_SDK. As best I can tell the Boot ROM always
defaults to UART0.

* Fixes debug UART selection for ets_putc

This addresses an issue of UART selection for ROM function ets_putc,
which is used by ::printf, ets_printf_P in core_esp_postmortem.cpp
and others. Currently ets_putc stays on UART0 after
Serial1.setDebugOutput(true) is called.

ets_putc() is not affected by calls to ets_install_putc1.
Its UART selection is controlled by the ROM function uart_buff_switch.

Updated uart_set_debug() to call uart_buff_switch whenever debug is
enabled on an UART. For the case of disabling, a call to select UART0
is made, because there is no disable option for this print method.

* Removed fp_putc_t typedef, save for a later PR

Author: mhightower83

cores/esp8266/esp8266_undocumented.h

@@ -11,6 +11,27 @@ extern int rom_i2c_readReg_Mask(int, int, int, int, int);
 
 extern int uart_baudrate_detect(int, int);
 
+/*
+ROM function, uart_buff_switch(), is used to switch printing between UART0 and
+UART1. It updates a structure that only controls a select group of print
+functions. ets_putc() and ets_uart_printf() are examples and are not affected by
+calls to ets_install_putc1().
+
+ Use:
+   0 for UART0, also clears RX FIFO
+   1 for UART1
+ */
+extern void uart_buff_switch(uint8_t);
+
+/*
+ ROM function, ets_uart_printf(), prints on the UART selected by
+ uart_buff_switch(). Supported format options are the same as vprintf(). Also
+ has cooked newline behavior. No flash format/string support; however, ISR safe.
+ Also, uses a static function in ROM to print characters which is only
+ controlled by uart_buff_switch().
+ */
+extern int ets_uart_printf(const char *format, ...) __attribute__ ((format (printf, 1, 2)));
+
 extern void ets_delay_us(uint32_t us);
 
 #ifdef __cplusplus