support 4-byte address format for VARIABLE_SIZE dummy flash device

This patch adds a support of 4-byte address format for VARIABLE_SIZE
dummy flash device, so that it can emulate an flash size larger than
16 MBytes.
- assigned a feature bits FEATURE_4BA to VARIABLE_SIZE flash config.
- added codes handling two commands, JEDEC_READ_4BA and
JEDEC_BYTE_PROGRAM_4BA.
- changed blockeraser to use Chip-Erase command so that it can be
free from flash address byte format.

TEST=ran the command line below:
$ flashrom -p dummy:image=${TMP_FILE},size=33554432, \
emulate=VARIABLE_SIZE -w ${IMG_32MB} -V -f

$ flashrom -p dummy:image=${TMP_FILE},size=16777216, \
emulate=VARIABLE_SIZE -w ${IMG_16MB} -V -f

$ flashrom -p dummy:image=${TMP_FILE},size=8388608, \
emulate=VARIABLE_SIZE -w ${IMG_8MB} -V -f

Signed-off-by: Namyoon Woo <namyoon@google.com>
Change-Id: Ia59eecfcbe798d50f8dacea98c3c508edf8ec77e
Reviewed-on: https://review.coreboot.org/c/flashrom/+/44881
Reviewed-by: Edward O'Callaghan <quasisec@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

flashchips.c

@@ -18765,13 +18765,14 @@ const struct flashchip flashchips[] = {
 		.model_id	= PROGDEV_ID,
 		.total_size	= 64,  /* This size is set temporarily */
 		.page_size	= 256,
+		.feature_bits	= FEATURE_4BA,
 		.tested		= TEST_OK_PREW,
 		.probe		= probe_variable_size,
 		.block_erasers	=
 		{
 			{
 				.eraseblocks = { {64 * 1024, 1} },
-				.block_erase = spi_block_erase_d8,
+				.block_erase = spi_block_erase_c7,
 			}
 		},
 		.write		= spi_chip_write_256,