mvebu: fix build regression due to neon-asm ghash module

mvebu: fix build regression due to neon-asm ghash module

This patch fixes the regression caused by adding the NEON
variant of the ghash as the default ghash package package:

> ERROR: module '[...]/arch/arm/crypto/ghash-arm-ce.ko' is missing.
> modules/crypto.mk:286: recipe for target
>  '[...]/kmod-crypto-ghash_4.19.106-1_aarch64_cortex-a53.ipk' failed

This patch limits the scope to the ARM32/cortexa9 target of mvebu.

Fixes: 285df63efc70 ("kernel: build neon-asm version of ghash module")
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>