efi_loader: correct CTRL-A - CTRL-Z console input

In the extended text input protocol CTRL-A - CTRL-Z have to be signaled as
Unicode characters a-z or A-Z depending on the shift state and not as 0x01
to 0x1a.

Update Python unit test.

This patch is required for using the EFI shell `edit` command.

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