GenFv: Arm: support images entered in Thumb mode

GenFv: Arm: support images entered in Thumb mode

Change GenFv for Arm architecture to generate a specific jump
instruction as image entry instruction, when the target entry label
is assembled with Thumb instruction set. This is possible since
SecCoreEntryAddress value fetched from the PE32 has its LSBit set when
the entry instruction executes in Thumb mode.

Signed-off-by: Etienne Carriere <etienne.carriere@linaro.org>
Acked-by: Liming Gao <gaoliming@byosoft.com.cn>
Reviewed-by: Sami Mujawar <sami.mujawar@arm.com>