Add support for selecting pin alternate functions from python.

Converts generted pins to use qstrs instead of string pointers.

This patch also adds the following functions:
pyb.Pin.names()
pyb.Pin.af_list()
pyb.Pin.gpio()

dir(pyb.Pin.board) and dir(pyb.Pin.cpu) also produce useful results.

pyb.Pin now takes kw args.

pyb.Pin.__str__ now prints more useful information about the pin
configuration.

I found the following functions in my boot.py to be useful:
```python
def pins():
    for pin_name in dir(pyb.Pin.board):
        pin = pyb.Pin(pin_name)
        print('{:10s} {:s}'.format(pin_name, str(pin)))

def af():
    for pin_name in dir(pyb.Pin.board):
        pin = pyb.Pin(pin_name)
        print('{:10s} {:s}'.format(pin_name, str(pin.af_list())))
```

1 files changed, 61 insertions, 0 deletions

diff --git a/teensy/pin_defs_teensy.c b/teensy/pin_defs_teensy.c
new file mode 100644
index 0000000000..dd2f0dc21f
--- /dev/null
+++ b/teensy/pin_defs_teensy.c
@@ -0,0 +1,61 @@
+#include <stdint.h>
+#include <mk20dx128.h>
+#include "mpconfig.h"
+#include "nlr.h"
+#include "misc.h"
+#include "qstr.h"
+#include "obj.h"
+#include "runtime.h"
+#include MICROPY_HAL_H
+#include "pin.h"
+
+// Returns the pin mode. This value returned by this macro should be one of:
+// GPIO_MODE_INPUT, GPIO_MODE_OUTPUT_PP, GPIO_MODE_OUTPUT_OD,
+// GPIO_MODE_AF_PP, GPIO_MODE_AF_OD, or GPIO_MODE_ANALOG.
+
+uint32_t pin_get_mode(const pin_obj_t *pin) {
+    volatile uint32_t *port_pcr = GPIO_PIN_TO_PORT_PCR(pin->gpio, pin->pin);
+    uint32_t pcr = *port_pcr;
+    uint32_t af = (*port_pcr & PORT_PCR_MUX_MASK) >> 8;;
+
+    if (af == 0) {
+        return GPIO_MODE_ANALOG;
+    }
+    if (af == 1) {
+        if (pin->gpio->PDDR & (1 << pin->pin)) {
+            if (pcr & PORT_PCR_ODE) {
+                return GPIO_MODE_OUTPUT_OD;
+            }
+            return GPIO_MODE_OUTPUT_PP;
+        }
+        return GPIO_MODE_INPUT;
+    }
+
+    if (pcr & PORT_PCR_ODE) {
+        return GPIO_MODE_AF_OD;
+    }
+    return GPIO_MODE_AF_PP;
+}
+
+// Returns the pin pullup/pulldown. The value returned by this macro should
+// be one of GPIO_NOPULL, GPIO_PULLUP, or GPIO_PULLDOWN.
+
+uint32_t pin_get_pull(const pin_obj_t *pin) {
+    volatile uint32_t *port_pcr = GPIO_PIN_TO_PORT_PCR(pin->gpio, pin->pin);
+
+    uint32_t pcr = *port_pcr;
+    if (pcr & PORT_PCR_PE) {
+        if (pcr & PORT_PCR_PS) {
+            return GPIO_PULLUP;
+        }
+        return GPIO_PULLDOWN;
+    }
+    return GPIO_NOPULL;
+}
+
+// Returns the af (alternate function) index currently set for a pin.
+
+uint32_t pin_get_af(const pin_obj_t *pin) {
+    volatile uint32_t *port_pcr = GPIO_PIN_TO_PORT_PCR(pin->gpio, pin->pin);
+    return (*port_pcr & PORT_PCR_MUX_MASK) >> 8;
+}