Platform/RPi3: Add acpiview to the builtin UEFI Shell

acpiview is a UEFI shell command that can be used to inspect and
validate ACPI tables from the pre-OS environment. Let's add it to
our build of the shell.

Signed-off-by: Pete Batard <pete@akeo.ie>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>