Wire up pkey_* and rseq syscalls on remaining architectures

Wire up pkey_* and rseq syscalls on remaining architectures

* linux/alpha/syscallent.h [524..527]: Wire up pkey_mprotect,
pkey_alloc, pkey_free, and rseq syscalls introduced on this architecture
by linux commit v5.1-rc1~160^2~3^2~3.
* linux/hppa/syscallent.h [351..354]: Likewise.
* linux/ia64/syscallent.h [1024 + 330..333]: Likewise.
* linux/m68k/syscallent.h [381..384]: Likewise.
* linux/sh/syscallent.h [384..387]: Likewise.
* linux/sparc/syscallent.h [362..365]: Likewise.
* linux/sparc64/syscallent.h: Likewise.
* linux/s390/syscallent.h [384..386]: Wire up pkey_mprotect,
pkey_alloc, and pkey_free syscalls introduced on this architecture
by linux commit v5.1-rc1~160^2~3^2~3.
* linux/s390x/syscallent.h: Likewise.
* linux/xtensa/syscallent.h [352]: Wire up rseq syscall introduced
on this architecture by linux commit v5.1-rc1~160^2~3^2~3.
* NEWS: Mention this.