Platforms/RaspberryPi: Fix BIOS Release Date and System Manufacturer

Per SMBIOS specs, The Type 0 BIOS Release Date is not a free form field but
must be specified in a US middle-endian format (mm/dd/yyyy), so make sure
we populate it accordingly by using the recently introduced TimeBaseLib
macros. This is required for platforms like Windows, that fail to parse the
date otherwise.

Also, the system manufacturer should not be set to the same value as the
board manufacturer for the Type 1 strings, as, on the Raspberry Pi, this is
not representative of the actual manufacturer of the system, which is the
Raspberry Pi Foundation always.

Signed-off-by: Pete Batard <pete@akeo.ie>
Reviewed-by: Leif Lindholm <leif@nuviainc.com>