riscv: Fix kernel crash due to PR_SET_TAGGED_ADDR_CTRL

In the Linux kernel, the following vulnerability has been resolved:

riscv: Fix kernel crash due to PR_SET_TAGGED_ADDR_CTRL

When userspace does PR_SET_TAGGED_ADDR_CTRL, but Supm extension is not

available, the kernel crashes:

Oops - illegal instruction [#1]

[snip]

epc : set_tagged_addr_ctrl+0x112/0x15a

ra : set_tagged_addr_ctrl+0x74/0x15a

epc : ffffffff80011ace ra : ffffffff80011a30 sp : ffffffc60039be10

[snip]

status: 0000000200000120 badaddr: 0000000010a79073 cause: 0000000000000002

set_tagged_addr_ctrl+0x112/0x15a

__riscv_sys_prctl+0x352/0x73c

do_trap_ecall_u+0x17c/0x20c

andle_exception+0x150/0x15c

Fix it by checking if Supm is available.