npcx: flash: Do not delay flash access requests.
npcx: flash: Do not delay flash access requests.

When depthcharge invokes a Host command that needs EC to access
flash, the response is delayed by approx 150 ms because EC is
busy with another flash operation to determine size of RW image
for computing hash. We can eliminate this delay and also speed up the
flash operation by using the same mechanism that is used for mec1322
based designs which also use external SPI flash.

The changes are:
a) We access 4 bytes from SPI flash at a time instead of a single byte
b) We split flash accesses into smaller parts which means that mutex lock
is acquired for a short duration.

BUG=chrome-os-partner:59875
BRANCH=none
TEST=make buildall -j
     After sysjump to RW, in EC Log the "hash start" is printed approx
     120 ms earlier.

Change-Id: Icb633379c992e795ba40eaf54fe9ec31747d4be6
Signed-off-by: Shamile Khan <0b4042e69ed1abbbdd05548f229cef643986e254@intel.com>
Reviewed-on: https://chromium-review.googlesource.com/426016
Reviewed-by: Shawn N <5259333ce42e3ace6a73988cec7115ed9d3a661a@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec