upxtreme: Add UP Xtreme support

UP Xtreme is based on the Intel(R) Core(TM) i3/i5/i7 Whiskey Lake SoCs.
The UP Xtreme presents one Raspberry Pi compatible HAT connector.

This implementaion supports i2c, spi, uart, adc and gpio through the
40pin HAT connector.

Gpio chardev capabilities have been disabled in this implementation. When
gpio chardev capabilities are enabled an input becomes unreadable after an
isr has been registered to the pin. See here for details:

https://github.com/intel-iot-devkit/mraa/issues/937

Tested on UP Xtreme, with UP Board Linux kernel 5.0.0
Features tested: gpio, gpio interrupts, i2c, spi, adc and uart.

Signed-off-by: Michael Campion <michael.campion@emutex.com>

include/x86/up_xtreme.h

@@ -0,0 +1,44 @@
+/*
+ * Author: Michael Campion <michael.campion@emutex.com>
+ * Based on work from: Dan O'Donovan <dan@emutex.com>
+ *                     Nicola Lunghi <nicola.lunghi@emutex.com>
+ * Copyright (c) 2019 Emutex Ltd.
+ * Copyright (c) 2014 Intel Corporation.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#pragma once
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include "mraa_internal.h"
+
+// +1 as pins are "1 indexed"
+#define MRAA_UPXTREME_PINCOUNT    (40 + 1)
+
+mraa_board_t*
+mraa_upxtreme_board();
+
+#ifdef __cplusplus
+}
+#endif