crypto: omap-aes - Kconfig: Add build support for AM437x

For AM437x SoC, ARCH_OMAP2 and ARCH_OMAP3 is not enabled in the defconfig. We
follow same thing as SHA driver, and add depends on ARCH_OMAP2PLUS so that the
config is selectable for AES driver on AM437x SoC builds.

Signed-off-by: Joel Fernandes <joelf@ti.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>