Add basic board build configurat for the SAML21 Xplained.  Initial commit is jsut the SAMD20 Xplained with name changes and does not yet build

Update the type passed to watchdog timer handlers.  Using uint32_t is a problem for 64-bit machines.

SAMD/L: Move content of chip/sam_memorymap.h to chip.h; move chip/sam_pinmap. to sam_pinmap.h for consistency with other header files

SAMA5 OHCI: Fix errors introduced with blind changes to match changes to LPC17 OHCI.  Fix some handling for the case where we get a falso alarm transfer completion after disconnection/cancellation

AT24 EEPROM driver.  Fix some an incorrect variable name used in conditional compilation.  SourceForge patch #55