OvmfPkg/Qemu: Fix various typos

OvmfPkg/Qemu: Fix various typos

Fix various typos in comments and documentation.

When "VbeShim.asm" is modified, we have to re-run "VbeShim.sh"
to update "VbeShim.h".
The string modified by this patch is only used when the DEBUG
macro (at the top of the file) is commented out. Since the
string is not referenced, NASM eliminates it, resulting in
the same byte array content in "VbeShim.h".

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Antoine Coeur <coeur@gmx.fr>
Reviewed-by: Philippe Mathieu-Daude <philmd@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Philippe Mathieu-Daude <philmd@redhat.com>
Message-Id: <20200207010831.9046-58-philmd@redhat.com>