KVM: fix exception entry / build bug, on 64-bit

-tip testing found this build bug:

 arch/x86/kvm/built-in.o:(.text.fixup+0x1): relocation truncated to fit: R_X86_64_32 against `.text'
 arch/x86/kvm/built-in.o:(.text.fixup+0xb): relocation truncated to fit: R_X86_64_32 against `.text'
 arch/x86/kvm/built-in.o:(.text.fixup+0x15): relocation truncated to fit: R_X86_64_32 against `.text'
 arch/x86/kvm/built-in.o:(.text.fixup+0x1f): relocation truncated to fit: R_X86_64_32 against `.text'
 arch/x86/kvm/built-in.o:(.text.fixup+0x29): relocation truncated to fit: R_X86_64_32 against `.text'

Introduced by commit 4ecac3fd

. The problem is that 'push' will default
to 32-bit, which is not wide enough as a fixup address. (and which would
crash on any real fixup event even if it was wide enough)

Introduce KVM_EX_PUSH to get the proper address push width on 64-bit too.

Signed-off-by: Ingo Molnar <mingo@elte.hu>