arch/arm: update VFPv2 comment to mention ARMv5

Commit 6b3a0417 ('arch/arm: arm926 may have VFP') forgot to update
the help text of the VFPv2 option to mention ARMv5. This commit fixes
that.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>