kernel: config: add symbol introduced with 6.1.82
Add CONFIG_MITIGATION_RFDS=y to the default config[1]
1. https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/diff/arch/x86/Kconfig?id=v6.1.82&id2=v6.1.81
Signed-off-by: John Audia <[email protected]>