RISC-V: Some Svpbmt fixes and cleanups

Some additionals comments and notes from autobuilders received after the
series got applied, warranted some changes.

* 'riscv-svpbmt' of ssh://gitolite.kernel.org/pub/scm/linux/kernel/git/palmer/linux:
  riscv: remove usage of function-pointers from cpufeatures and t-head errata
  riscv: make patch-function pointer more generic in cpu_manufacturer_info struct
  riscv: Improve description for RISCV_ISA_SVPBMT Kconfig symbol
  riscv: drop cpufeature_apply_feature tracking variable
  riscv: fix dependency for t-head errata