powerpc/corenet: enable CONFIG_I2C_MUX and CONFIG_I2C_MUX_PCA954x

By default we enable CONFIG_I2C_MUX and CONFIG_I2C_MUX_PCA954x,
which are needed on T2080QDS, T4240QDS, B4860QDS, etc.

Signed-off-by: Shengzhou Liu <Shengzhou.Liu@freescale.com>
[scottwood@freescale.com: fixed subject line]
Signed-off-by: Scott Wood <scottwood@freescale.com>

diff --cc arch/powerpc/configs/corenet32_smp_defconfig
Simple merge

diff --cc arch/powerpc/configs/corenet64_smp_defconfig
Simple merge