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>

test/py/tests/test_efi_selftest.py

@@ -141,7 +141,7 @@ def test_efi_selftest_text_input_ex(u_boot_console):
 	u_boot_console.run_command(cmd=chr(4), wait_for_echo=False,
 				   send_nl=False, wait_for_prompt=False)
 	m = u_boot_console.p.expect(
-		['Unicode char 4 \(unknown\), scan code 0 \(CTRL\+Null\)'])
+		['Unicode char 100 \\(\'d\'\\), scan code 0 \\(CTRL\\+Null\\)'])
 	if m != 0:
 		raise Exception('EOT failed in \'text input\' test')
 	u_boot_console.drain_console()