ArmPlatformPkg/Bds: Introduced helper function to detect if an Ascii/Unicode string...

ArmPlatformPkg/Bds: Introduced helper function to detect if an Ascii/Unicode string is printable

Some limitations:
 - it only supports unicode string that use ASCII character (< 0x100)
 - single character ASCII strings are interpreted as Unicode string
 - string cannot be longer than 2 x BOOT_DEVICE_OPTION_MAX (600 bytes)

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Olivier Martin <olivier.martin@arm.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@15455 6f19259b-4bc3-4df7-8a09-765794883524