davinci: introduce support for AM1x ARM9 microprocessors

The Sitara AM17x SoCs from TI are an OMAP-L137 pin-to-pin
compatible ARM9 microprocessor offering from TI.

The Sitara AM18x SoCs from TI are an OMAP-L138 pin-to-pin
compatible ARM9 microprocessor offering from TI.

More information about these processors available at:
www.ti.com/am1x

Because of their compatibiliy with OMAP-L1x, the kernel
support for OMAP-L1x is fully relevant to AM1x processors.

This patch updates the Kconfig prompt and help text to include
the AM1x part names to help users select configurations required
for these parts easily.

Also, the hardware information that shows up in /proc/cpuinfo
is updated to show applicability of the respective OMAP-L1x EVMs
for AM1x parts.

Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>