kernel: add missing STMMAC options in generic configs

STMMAC_PLATFORM and STMMAC_PCI have been added recently in the kernel,
but show up only when STMMAC driver is enabled. So se'll add it in the
generic config, so the kernel build doesn't stall whenever we enable
this driver.

Signed-off-by: Mathieu Olivari <mathieu@codeaurora.org>
SVN-Revision: 45828