drivers/vpd: add framework to search VPD in romstage

Summary:
Added a framework to search VPD in romstage before memory is
avilable. vpd_cbmem.c and vpd_premem.c are added for
code specific for premem environment and for environment that
cbmem can be used.

Since global variable is forbidden in romstage. A CAR_GLOBAL
variable is defined in vpd.c. This variable holds VPD binary
blobs' base address and size from memory mapped flash.

The overall flow is:
* The CAR variable g_vpd_blob is initialized if it was not,
either at romstage (before FSP-M execution in case of FSP UPD
customization), or at ramstage.
* At ramstage, during CBMEM_INIT, the VPD binary blob contents
are copied into CBMEM.
* At vpd_find() which may be called at romstage or at ramstage,
it sets storage for a local struct vpd_blob variable.
  * The variable gets contents duplicated from g_vpd_blob, if
vpd_find() is called at romstage.
  * The variable gets contents obtained from CBMEM, if vpd_find()
is called at ramstage.

Added a call vpd_get_bool(). Given a key/value pair in VPD
binary blob, and name of a bool type variable, set the variable
value if there is a match.
Several checks are in place:
* The key/value length needs to be correct.
* The key name needs to match.
* THe value is either '1' or '0'.

Test Plan:
* Build an OCP MonoLake coreboot image, flash and run.

Tags:
Signed-off-by: Jonathan Zhang <jonzhang@fb.com>
Change-Id: Iebdba59419a555147fc40391cf17cc6879d9e1b2
Reviewed-on: https://review.coreboot.org/c/coreboot/+/34634
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Hung-Te Lin <hungte@chromium.org>

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