ARM: omap2plus_defconfig: Enable ARM_KERNMEM_PERMS and few loadable modules

With recent omap assembly fixes for CONFIG_DEBUG_RODATA, we can
now use DEBUG_RODATA. Let's enable ARM_KERNMEM_PERMS so that
DEBUG_RODATA gets selected by default. This way we can make sure
any related issues are caught early.

And while testing things on various devices, I noticed we're
missing few loadable modules to make things more usable:

- USB Ethernet for smsc75xx, we only have smsc97xx right now

- Basic USB serial drivers for things like ftdi and pl2303 ports

- Blinking leds with pca963x

Signed-off-by: Tony Lindgren <tony@atomide.com>