loader.efi: fix console output after BS off

When Boot Services (BS) are switched off, we can not use BS
functions any more. Since drawn console does implement our own
Blt(), we can use it to draw the console.

However, SimpleTextOutput protocol based console output must be
blocked.

Tested by inserting printf() after ExitBootServices() call.

(cherry picked from commit 4c7a3a70e047fbba2a3ce4a0168eaf2baddca76b)