x86/entry/64: Use JMP instead of JMPQ

x86/entry/64: Use JMP instead of JMPQ

Somehow the swapgs mitigation entry code patch ended up with a JMPQ
instruction instead of JMP, where only the short jump is needed.  Some
assembler versions apparently fail to optimize JMPQ into a two-byte JMP
when possible, instead always using a 7-byte JMP with relocation.  For
some reason that makes the entry code explode with a #GP during boot.

Change it back to "JMP" as originally intended.

Fixes: 18ec54fdd6d1 ("x86/speculation: Prepare entry code for Spectre v1 swapgs mitigations")
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
CVE-2019-1125

(backported from commit 64dbc122b20f75183d8822618c24f85144a5a94d)
[tyhicks: Adjust context in entry_64.S]
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>