BaseTools: Update Expression.py for VOID* to support L'a' and 'a'

BaseTools: Update Expression.py for VOID* to support L'a' and 'a'

Original VOID* type support L"string" and "string" format, now we also
add support for single quote string that without null terminator.
Type VOID* support L'a' and 'a', the value transfer to c style value.
L'a' --> {0x61, 0x00}
L'ab' --> {0x61, 0x00, 0x62, 0x00}
'a'  --> {0x61}
'ab' --> {0x61, 0x62}

when the value is L'' or '' that not include any character, tool will
report error.

Cc: Liming Gao <liming.gao@intel.com>
Cc: Yonghong Zhu <yonghong.zhu@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Yunhua Feng <yunhuax.feng@intel.com>
Reviewed-by: Yonghong Zhu <yonghong.zhu@intel.com>