support 4-byte address format for VARIOUS_SIZE dummy flash device

This patch adds a support of 4-byte address format for VARIOUS_SIZE
dummy flash device, so that it can emulate an flash size larger than
16 MBytes.
- assigned a feature bits FEATURE_4BA to VARIOUS_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
---
M dummyflasher.c
M flashchips.c
2 files changed, 25 insertions(+), 3 deletions(-)