ARM: at91: merge all SOC_AT91SAM9xxx

ARM: at91: merge all SOC_AT91SAM9xxx

Only use SOC_AT91SAM9 for all the at91sam9 SoCs. It removes all the empty
at91sam9xxx.c SoC files. It also removes the useless at91_init_soc affectation
procedure and its "init" function pointer.
Only the SoC detection and display are kept for the at91sam9:
at91_soc_is_enabled() and at91_boot_soc.map_io() function calls are also
removed.

It enables HAVE_AT91_SMD and HAVE_AT91_UTMI for all the sam9 SoCs but this only
represents 96 bytes of uncompressed kernel code.

Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
[nicolas.ferre@atmel.com: different organization of the patches]
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>