sys/linux: add more amd64/riscv64 special addresses
sys/linux: add more amd64/riscv64 special addresses

Add VSYSCALL_ADDR, PAGE_OFFSET, VMEMMAP addresses.

xairy/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller,google/syzkaller