cpu/arm/k60: Add RTC driver.

Broke out RTC stuff from other parts and added support for the seconds
counter.
Removed old unused core-clocks.c (code is now in system_MK60D10.c)

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>
cpu/arm/k60: Implement newlib syscalls.

All newlib syscalls are somewhat implemented now. File IO is split into
device IO and actual file IO based on fd number. File IO is mapped to
CFS functions, device IO is mapped using a platform device operations
table. stdin, stdout, stderr is currently mapped to UART1.

See also: http://neptune.billgatliff.com/newlib.html

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>
cpu/arm/k60: isatty: Set ENOTTY.

Set errno = ENOTTY when isatty is called with a non-tty fd.

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>
cpu/arm/k60: Rework _open_r flags handling.

Just to make sure the case where flags = O_WRONLY|O_RDONLY works the
same as O_RDWR.

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>
cpu/arm/k60: Add checks for invalid fd.

Add checks for fd less than zero in newlib syscalls for files, prevents
bugs where devoptab[-1] etc may be attempted to be read as if they are
valid device operation entries.

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>
cpu/arm/k60: Refactor UART driver.

Major refactoring of UART driver:
 - Replaced UART_Type *uart_dev with unsigned int uart_num. No CPU
   specific pointers needed to call the UART functions.
 - Added support for automatically determining the current module clock
   frequency during uart_init().
 - Added uart_num parameter to uart_enable_rx_interrupt() and
   uart_set_rx_callback().
 - Support for RX interrupts on UARTs 0-5 (untested)
 - Support for TX buffering on all UARTs 0-5 (untested)
 - Some const-correctness fixes in UART driver API.
 - SLIP connection is using POSIX file API for handling writes. The
   SLIP driver is not yet completely decoupled from UART module, but a
   long term goal is to allow choosing between UART and other methods
   of opening a point to point link, for example USB-CDC, by simply
   modifying a #define in contiki-conf.h.
 - Removed dead printf_putc in contiki-main.c.
 - Added default buffer size UART_CONF_DEFAULT_TXBUFSIZE.
 - Added explanation for UART1_CONF_TXBUFSIZE.
 - Added #if UARTx_CONF_ENABLE preprocessor checks for each UART module
   ISR and TX buffer definition.
core/net/ip/slipdev: Remove unnecessary cast.

Remove unnecessary cast to char * and makes a warning go away. Gave
a warning previously:

    ../../../core/net/ip/slipdev.c:106:11: warning: assigning to
          'uint8_t *' (aka 'unsigned char *') from 'char *' converts
          between pointers to integer types with different sign
          [-Wpointer-sign]
          ptr = (char *)uip_appdata;
              ^ ~~~~~~~~~~~~~~~~~~~

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>