ANDROID: arm64: add __va_function

With CFI, the compiler replaces function references with pointers
to the CFI jump table. This breaks passing these addresses to
code running at EL2, where the jump tables are not valid. Add a
__va_function macro similarly to the earlier __pa_function to take
address of the actual function in inline assembly and use that in
kvm_ksym_ref instead.

Bug: 163385976
Change-Id: I097b99409995512c00786300e7d18fe42c720a1b
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>