ARM: at91: mark const init data with __initconst instead of __initdata

As long as there is no other non-const variable marked __initdata in the
same compilation unit it doesn't hurt. If there were one however
compilation would fail with

error: $variablename causes a section type conflict

because a section containing const variables is marked read only and so
cannot contain non-const variables.

Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
[nicolas.ferre@atmel.com: update the paths after having re-arranged the patches]
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>