The problem seems to be rooted in the firmware. The watchdog timer interrupt is 0 which corresponds to an IPI after commit 64b499d8df40. The zero GSI for the watchdog is clearly wrong but was harmless (except for non-functioning WDT) until now when it break IPI0.
As noted in comment 1 this is a firmware issue. There is a workaround with a command line option, so I see no need to clutter up the kernel code with some sort of quirk for EOL platforms. So to work around this, add "initcall_blacklist=gtdt_sbsa_gwdt_init" to the kernel command line.