configs: at91: sam9x60: Switch to new reset driver

Since commit 61040097 ("reset: at91: Add reset driver for basic
assert/deassert operations") the compatible "microchip,sam9x60-rstc" for
the sam9x60 reset controller in sam9x60.dtsi is not handled by
CONFIG_SYSRESET_AT91 anymore, but by CONFIG_RESET_AT91 now.  This
resulted in the following error message, when trying to reset from
U-Boot shell:

    U-Boot> reset
    resetting ...
    System reset not supported on this platform
    ### ERROR ### Please RESET the board ###

Fixed by enabling the new driver in the relevant defconfigs.  Tested on
sam9x60-curiosity board.  Defconfigs for sam9x60ek adapted in the same
way, but without testing.  These should be all sam9x60 boards affected
in U-Boot here.

Signed-off-by: Alexander Dahl <ada@thorsis.com>