efi_selftest: Add geometric shapes character selftest

Draw symbols from Unicode's "Geometric shapes" page which translate to
code page 437 code points 1-31. These are used by UEFI applications to
draw user interfaces using EFI_SIMPLE_TEXT_OUTPUT_PROTOCOL.
The output has to be checked manually on the screen for correctness.

Signed-off-by: Janne Grunau <j@jannau.net>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>