This supports three types GD32 FMC flash memory. GD32 FMC v1,
GD32 FMC v2 and GD32 FMC v3.
GD32 FMC v1 for small flash memory, flash size can be up to 512KB.
GD32 FMC v2 for large flash memory, flash size can be up to 3072KB.
GD32 FMC v3 not use page but sector as minimum block, flash size can
be up to 3072KB.
Signed-off-by: HaiLong Yang <hailong.yang@brainco.cn>
