Added --multibyte_chars option

Added --multibyte_chars option for ARM and uARM build.

This enables to use multi-byte character such as Japanese or Chinese
especially for string literal.
It should not be affected single-byte character set.  Tested with
Japanese Windows environment.
Merge remote-tracking branch 'upstream/master'
Fixed L6235E link error for NRF51822 variants

Changed TARGET_NRF51822 target directory names to TARGET_MCU_NRF51822
Removed NRF51822 names to extra_label of target.py
Added MCU_NRF51822 names to extra_label of target.py
Tested with blinky example for NRF51822, HRM1017, ARCH_BLE and
RBLAB_NRF51822 target
Revert "Fixed L6235E link error for NRF51822 variants"

This reverts commit 320e384f020917fe0488740d8bed0dfde4d1b242.
Merge pull request #420 from toyowata/master

Added --multibyte_chars option