alpha: support R_ALPHA_REFLONG relocations for module loading

Since commit 71810db2

 (modversions: treat symbol CRCs
as 32 bit quantities) R_ALPHA_REFLONG relocations can be required
to load modules. This implements it.

Tested-by: Bob Tracy <rct@gherkin.frus.com>
Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Michael Cree <mcree@orcon.net.nz>
Signed-off-by: Matt Turner <mattst88@gmail.com>