openblas: SPARC support is for Sparc v9

Makefile.sparc in the openblas source code passes -mcpu=v9, i.e it
assumes a SPARCv9 CPU. Therefore, this commit adjusts openblas
Config.in file so that SPARC is only used for BR2_sparc_v9.

Fixes:

  http://autobuild.buildroot.net/results/805087e87b8bb7d11adb49d9eca3959a37aca3a2/



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>