build_image: Add command line arg `chromeos_pstore.ecc_size=4` for x86

This change adds a kernel command line argument
`chromeos_pstore.ecc_size` for x86 platforms.

`ecc_size=4` is set as the default value, following go/cros-ecc-rollout.
As chromeos_pstore is x86-specific driver, this changes affects solely
to x86 platforms.

BUG=b:413292019
TEST=build image for x86 platform and check config.txt for this argument

Change-Id: Ibfc6c4118cb9f080d87d0111add06a12c8537f6b
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosutils/+/6664609
Tested-by: Naoya Tezuka <naoyatezuka@google.com>
Reviewed-by: Gilberto Contreras <gcontreras@google.com>
Commit-Queue: Naoya Tezuka <naoyatezuka@google.com>
diff --git a/build_kernel_image.sh b/build_kernel_image.sh
index e843e20..ae92a85 100755
--- a/build_kernel_image.sh
+++ b/build_kernel_image.sh
@@ -291,6 +291,7 @@
 add_efi_memmap
 noresume
 i915.modeset=1
+chromeos_pstore.ecc_size=4
 EOF
 elif [[ "${FLAGS_arch}" != "arm" && "${FLAGS_arch}" != "mips"  && "${FLAGS_arch}" != "arm64" ]]; then
   error "Unknown arch: ${FLAGS_arch}"