Revert "mach:hwmod: disable uart3 warnings"

This reverts commit 6b45d006eacef232aa1864cbe2a77bf05d94f7f5.
Revert "mach: prevent disabling uart clock"

This reverts commit 641e63b22a2e6697f1a2acc96c5264db66e3ea4d.
Revert "mach: prevent UART3 from being disabled by the hwmod"

This reverts commit fc40e813396bd809264baa525946da638f073f11.
defconfig: switch to preemptible RCU