vboot: Plumb the two disk sizes and external GPT param through

This patch reinstates the external GPT support which was previously
committed and reverted. Improvements since last time include:
- Cleaned-up internal interface based on code review
- Function correctly on legacy bootloaders (e.g., depthcharge before
  NAND-related patches are added)
- Better comments
- Treat new field values = 0 -> not use new feature
- Tests are added to ensure external GPT flag is passed down properly
The original commit had change-id
I5a77e417aea8ee9442d18c200d1b073aa5375ecf
Its commit message is reproduced below, and then an additional test.
----
To support an external GPT, disks have two new attributes:
- A binary flag indicating whether the GPT is in the same address
  space as the payloads or a separate one.
- The number of sectors of the streaming portion of storage, as
  opposed to the portion containing the GPT.
These have been added elsewhere to GptData (in cgptlib) and BlockDev
(in depthcharge). This patch adds the plumbing between those, including
in the DiskInfo interface between the firmware and vboot.
BUG=chromium:425677
BRANCH=none
TEST=Interactively wrote the GPT with cgpt and observed the following
boot with depthcharge to read the GPT from SPI and then read from
the proper locations in NAND flash.
TEST=make runalltests passes.
TEST=boots from USB with depthcharge from HEAD.

Change-Id: Ia7956517a7b9da0301f01fac5a10204f6d78cf4f
Signed-off-by: Dan Ehrenberg <dehrenberg@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/234640
Reviewed-by: Bill Richardson <wfrichar@chromium.org>

firmware/lib/include/load_kernel_fw.h

@@ -16,9 +16,11 @@
 
 /* Boot flags for LoadKernel().boot_flags */
 /* Developer switch is on */
-#define BOOT_FLAG_DEVELOPER (0x01ULL)
+#define BOOT_FLAG_DEVELOPER    (0x01ULL)
 /* In recovery mode */
-#define BOOT_FLAG_RECOVERY  (0x02ULL)
+#define BOOT_FLAG_RECOVERY     (0x02ULL)
+/* GPT is external */
+#define BOOT_FLAG_EXTERNAL_GPT (0x04ULL)
 
 typedef struct LoadKernelParams {
 	/* Inputs to LoadKernel() */
@@ -40,8 +42,10 @@ typedef struct LoadKernelParams {
 	VbExDiskHandle_t disk_handle;
 	/* Bytes per lba sector on current device */
 	uint64_t bytes_per_lba;
-	/* Last addressable lba sector on current device */
-	uint64_t ending_lba;
+	/* Number of LBA-addressable sectors on the main device */
+	uint64_t streaming_lba_count;
+	/* Random-access GPT size */
+	uint64_t gpt_lba_count;
 	/* Destination buffer for kernel (normally at 0x100000) */
 	void *kernel_buffer;
 	/* Size of kernel buffer in bytes */