Documentation/Intel: Add NativeRaminit documentation

Add documentation for Intel native raminit on Intel SandyBridge.
Documented so far:
* Register
* Read training
* Frequency selection
* SMBIOS type 17 memory reporting
* Various Kconfig options and features

Change-Id: I3b977460ecb29c9a54e3fab82349982fca9918e7
Signed-off-by: Patrick Rudolph <siro@das-labor.org>
Reviewed-on: https://review.coreboot.org/22275
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
9 files changed