nrf: add support for the PineTime64 devkit

This smartwatch doesn't have an on-board debugger, so I picked the one I
was using while getting this smartwatch to run Go programs (the J-Link
EDU Mini).

src/machine/board_pinetime-devkit0.go

@@ -0,0 +1,61 @@
+// +build pinetime_devkit0
+
+package machine
+
+// Board pins for the PineTime.
+// Details: https://wiki.pine64.org/index.php/PineTime
+
+// The PineTime has a low-frequency (32kHz) crystal oscillator on board.
+const HasLowFrequencyCrystal = true
+
+// LEDs simply expose the three brightness level LEDs on the PineTime. They can
+// be useful for simple "hello world" style programs.
+const (
+	LED  = LED1
+	LED1 = LCD_BACKLIGHT_HIGH
+	LED2 = LCD_BACKLIGHT_MID
+	LED3 = LCD_BACKLIGHT_LOW
+)
+
+// UART pins for PineTime. Note that RX is set to NoPin as RXD is not listed in
+// the PineTime schematic 1.0:
+// http://files.pine64.org/doc/PineTime/PineTime%20Port%20Assignment%20rev1.0.pdf
+const (
+	UART_TX_PIN Pin = 11 // TP29 (TXD)
+	UART_RX_PIN Pin = NoPin
+)
+
+// SPI pins for the PineTime.
+const (
+	SPI0_SCK_PIN  Pin = 2
+	SPI0_MOSI_PIN Pin = 3
+	SPI0_MISO_PIN Pin = 4
+)
+
+// I2C pins for the PineTime.
+const (
+	SDA_PIN Pin = 6
+	SCL_PIN Pin = 7
+)
+
+// Button pins. For some reason, there are two pins for the button.
+const (
+	BUTTON_IN  Pin = 13
+	BUTTON_OUT Pin = 15
+)
+
+// Pin for the vibrator.
+const VIBRATOR_PIN Pin = 16
+
+// LCD pins, using the naming convention of the official docs:
+// http://files.pine64.org/doc/PineTime/PineTime%20Port%20Assignment%20rev1.0.pdf
+const (
+	LCD_SCK                = SPI0_SCK_PIN
+	LCD_SDI                = SPI0_MOSI_PIN
+	LCD_RS             Pin = 18
+	LCD_CS             Pin = 25
+	LCD_RESET          Pin = 26
+	LCD_BACKLIGHT_LOW  Pin = 14
+	LCD_BACKLIGHT_MID  Pin = 22
+	LCD_BACKLIGHT_HIGH Pin = 23
+)