Convert CONFIG_AT91SAM9260 et al to Kconfig

This converts the following to Kconfig:
   CONFIG_AT91SAM9260
   CONFIG_AT91SAM9G20
   CONFIG_AT91SAM9XE
   CONFIG_AT91SAM9261
   CONFIG_AT91SAM9263
   CONFIG_AT91SAM9G45
   CONFIG_AT91SAM9M10G45
   CONFIG_AT91SAM9N12
   CONFIG_AT91SAM9RL
   CONFIG_AT91SAM9X5
   CONFIG_SAM9X60
   CONFIG_SAMA7G5
   CONFIG_SAMA5D2
   CONFIG_SAMA5D3
   CONFIG_SAMA5D4

These options are already select'd as needed, so we're just cleaning up
files here.

Cc: Eugen Hristev <eugen.hristev@microchip.com>
Signed-off-by: Tom Rini <trini@konsulko.com>