efi_loader: check lowest supported version

The FMP Payload Header which EDK II capsule generation scripts
insert has a firmware version.
This commit reads the lowest supported version stored in the
device tree, then check if the firmware version in FMP payload header
of the ongoing capsule is equal or greater than the
lowest supported version. If the firmware version is lower than
lowest supported version, capsule update will not be performed.

Signed-off-by: Masahisa Kojima <masahisa.kojima@linaro.org>