arm64: record the use of x8 as of vex r2938.


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14389 a5019735-40e9-0310-863c-91ae7b9d1cf9
diff --git a/docs/internals/register-uses.txt b/docs/internals/register-uses.txt
index 4835d23..a57192a 100644
--- a/docs/internals/register-uses.txt
+++ b/docs/internals/register-uses.txt
@@ -143,7 +143,7 @@
 r0                    int#0      ret#0 (??)
 r1                    int#1      ret#1 (??)
 r2-7                  int#2..7 
-r8                              "Indirect res loc reg"
+r8                              "Indirect res loc reg" ProfInc scratch
 r9                              "Temporary regs"      chaining scratch
 r10-15                          "Temporary regs"      avail
 r16(IP0)