RISC-V: Remove svvptc from riscv-ext-bitmask.def

There should be no svvptc in the riscv-ext-bitmask.def file since it has
not yet been added to the RISC-V C API Specification or the Linux
hwprobe. And there is no need for userspace software to know that this
extension exists. So remove it from the riscv-ext-bitmask.def file.

Fixes: e4f4b2dc ("RISC-V: Minimal support for svvptc extension.")
Signed-off-by: Yangyu Chen <cyy@cyyself.name>

gcc/ChangeLog:

	* common/config/riscv/riscv-ext-bitmask.def (RISCV_EXT_BITMASK): Remove svvptc.