platform: generic: thead: separate T-Head PMU Errata

platform: generic: thead: separate T-Head PMU Errata

As Guo Ren said from the kernel mailing list [1], future T-Head CPUs,
including the newer versions of T-Head C908, will feature standard
Sscofpmf extension. For these CPUs, T-Head's implementation of PMU
Overflow Interrupts may not needed anymore. In this case, we shouldn't
apply T-Head PMU for all T-Head CPUs. Thus, this patch separated T-Head PMU
errata.

[1] https://lore.kernel.org/linux-riscv/Zh9sUUUT09LZb0MO@gmail.com/

Signed-off-by: Yangyu Chen <cyy@cyyself.name>
Reviewed-by: Inochi Amaoto <inochiama@outlook.com>
Reviewed-by: Anup Patel <anup@brainfault.org>