mfd: altera: merge ARCH_SOCFPGA and ARCH_STRATIX10

Simplify 32-bit and 64-bit Intel SoCFPGA Kconfig options by having only
one for both of them.  This the common practice for other platforms.
Additionally, the ARCH_SOCFPGA is too generic as SoCFPGA designs come
from multiple vendors.

The side effect is that the MFD_ALTERA_A10SR will now be available for
both 32-bit and 64-bit Intel SoCFPGA, even though it is used only for
32-bit.

Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>