firmware: Google VPD: import lib_vpd source files

This patch imports lib_vpd.h and vpd_decode.c from the Chromium Vital
Product Data project.

This library is used to parse VPD sections obtained from coreboot table
entries describing Chromebook devices product data. Only the sections of
type VPD_TYPE_STRING are decoded.

The VPD string sections in the coreboot tables contain the type (1 byte
set to 0x01 for strings), the key length, the key ascii array, the value
length, and the value ascii array. The key and value arrays are not null
terminated.

Signed-off-by: Wei-Ning Huang <wnhuang@google.com>
Signed-off-by: Thierry Escande <thierry.escande@collabora.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>