elf(5): mention the ELF machine type EM_AARCH64

[Kevin Lo]

ok?

Index: share/man/man5/elf.5
===================================================================
RCS file: /cvs/src/share/man/man5/elf.5,v
retrieving revision 1.34
diff -u -p -u -p -r1.34 elf.5
--- share/man/man5/elf.5        27 Oct 2017 08:36:42 -0000      1.34
+++ share/man/man5/elf.5        17 Jun 2019 06:46:19 -0000
@@ -325,6 +325,8 @@ Intel IA-64.
 AMD64.
 .It Dv EM_VAX
 DEC Vax.
+.It Dv EM_AARCH64
+ARM 64-bit.
 .It Dv EM_ALPHA_EXP
 Compaq [DEC] Alpha with enhanced instruction set.
 .El