arc770: update kernel version to 5.4

arc770: update kernel version to 5.4

Update config with make kernel_oldconfig and copy/refresh patch.

Add CONFIG_WATCHDOG_CORE=y to fix the following error as done for
several targets already:

 Package kmod-hwmon-sch5627 is missing dependencies for the following
 libraries:
 watchdog.ko

Directly switch to kernel 5.4.

This patch is compile-tested only. However, the target is essentially
pure upstream with a single patch, and it has been reported that
kernel 5.4 has been run on this target successfully already.

Note that in my local tests building with all packages/kmods failed
since openvswitch selects libunwind, which doesn't build for arc with
the following error:

checking if we should build libunwind-ptrace... yes
checking if we should build libunwind-setjmp... yes
checking for build architecture... x86_64
checking for host architecture... arc
checking for target architecture... arc
checking for target operating system... linux-gnu
checking for ELF helper width... configure: error: Unknown ELF target: arc
make[3]: *** [Makefile:65: /data/openwrt/build_dir/target-arc_arc700_uClibc/
   libunwind-1.3.1/.configured_68b329da9893e34099c7d8ad5cb9c940] Error 1

Deselecting all kmod-openvswitch* packages will have the build run through.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>