dpkg 1.22.0 started adding -mbranch-protection=standard on arm64. This
breaks cross builds for arm64 which add CFLAGS to CC_FOR_BUILD
invocations as well because CFLAGS are assembled for the host
architecture and might break build architecture compiler invocations.

These two patches will be 6.6 material but it makes sense to backport
them. The first patch will reduce FE idle memory traffic to 512 KB/s.
The second patch makes devcoredumps from etnaviv more reliable.

Signed-off-by: Christian Gmeiner <cgmeiner@igalia.com>

linux/build.sh: re-enable copying pocket reform dts (disabled in 'initial support for meson-g12b-bananapi-cm4-mnt-reform2')