Don't assume FRU MCU memory locations for the FRU data fields, or their sizes,
instead read and interpret the IPMI data, as stipulated in the IPMI spec
version 1.0 rev 1.2.

Extract the Product Name, Product Part/Model Number, and the Product Serial
Number by interpreting the IPMI data.

Check the checksums of the stored IPMI data to make sure we don't read and
give corrupted data back the the user.

Eliminate small I2C reads, and instead read the whole Product Info Area in one
go, and then extract the information we're seeking from it.

Eliminates a whole function, making this file smaller.

v2: Clarify changes in the commit message.

Cc: Alex Deucher <Alexander.Deucher@amd.com>
Cc: Kent Russell <kent.russell@amd.com>
Signed-off-by: Luben Tuikov <luben.tuikov@amd.com>
Tested-by: Kent Russell <kent.russell@amd.com>
Reviewed-by: Kent Russell <kent.russell@amd.com>
Reviewed-by: Alex Deucher <Alexander.Deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>