Updated default config with new sym (CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY=y).

Manually rebased:
    generic/hack-5.10/220-arm-gc_sections.patch

All other patches automatically rebased.

Build system: x86_64
Build-tested: bcm2711/RPi4B, mt7622/RT3200
Run-tested: bcm2711/RPi4B, mt7622/RT3200

Signed-off-by: John Audia <graysky@archlinux.us>