drivers/smmstore: Implement SMMSTORE version 2

SMMSTORE version 2 is a complete redesign of the current driver. It is
not backwards-compatible with version 1, and only one version can be
used at a time.

Key features:
* Use a fixed communication buffer instead of writing to arbitrary
  memory addresses provided by untrusted ring0 code.
* Give the caller full control over the used data format.
* Split the store into smaller chunks to allow fault tolerant updates.
* Don't provide feedback about the actual read/written bytes, just
  return error or success in registers.
* Return an error if the requested operation would overflow the
  communication buffer.

Separate the SMMSTORE into 64KiB blocks that can individually be
read/written/erased. To be used by payloads that implement a
FaultTolerant Variable store like TianoCore.

The implementation has been tested against EDK2 master.

An example EDK2 implementation can be found here:
https://github.com/9elements/edk2-1/commit/eb1127744a3a5d5c8ac4e8eb76f07e79c736dbe2

Change-Id: I25e49d184135710f3e6dd1ad3bed95de950fe057
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Signed-off-by: Christian Walter <christian.walter@9elements.com>
---
M Documentation/drivers/index.md
A Documentation/drivers/smmstorev2.md
M payloads/libpayload/include/coreboot_tables.h
M src/commonlib/include/commonlib/cbmem_id.h
M src/commonlib/include/commonlib/coreboot_tables.h
M src/drivers/smmstore/Kconfig
M src/drivers/smmstore/Makefile.inc
A src/drivers/smmstore/ramstage.c
M src/drivers/smmstore/smi.c
M src/drivers/smmstore/store.c
M src/include/smmstore.h
M src/lib/coreboot_table.c
12 files changed, 697 insertions(+), 5 deletions(-)