efi_selftest: test EFI_BLOCK_IO_PROTOCOL.Media->LastBlock

The field Media->LastBlock of the EFI_BLOCK_IO_PROTOCOL must be filled
with the index of the last logical block (LBA) for the block device that
our test driver provides.

After calling ConnectController() U-Boot exposes the block IO protocol for
the partition check that the value of Media->LastBlock equals the partition
size minus one.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>