SAML21-Xplained:  Update the cloned SAMD20-Xplained board configuration for specifics of the SAML21-Xplained

SAMD/L: Hide differences in the way peripheral clocking is enabled behind macros.  Some updates to saml_clockconfig.h + various fixes while working toward SAML21 build

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

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

Rename SAMD directories and configuration variables to SAMDL so that the same build environment can support the SAML

SAMV71-XULT: Reads from LCD memory do not work.  Change configuration so that the LCD is treated as write-only

Adds board support for the Teensy LC board.  Support is based off the Freedom KL25Z board. LED, PWM, and UART0 have been tested. The SPI pins are mapped correctly but have not yet been tested.  From Michael Hope as SourceForge patch 51.

LPC17 USB host: Fix some compile errors when bulk endpoints + USB debug enabled.  Refresh a configuration

Rename usbhost_storageinit() to usbhost_msc_initialize().  Add calls to usbhost_cdcacm_initialize() is CONFIG_USBHOST_CDCACM is selected.

SAMA5D OHCI: Remove a local variable that is unused when debug is disabled; refresh a configuration.  Update a README