ARM: davinci: mark spi_board_info arrays as const

Building with LTO revealed that three spi_board_info arrays are marked
__initconst, but not const:

arch/arm/mach-davinci/board-dm365-evm.c: In function 'dm365_evm_init':
arch/arm/mach-davinci/board-dm365-evm.c:729:30: error: 'dm365_evm_spi_info' causes a section type conflict with 'dm646x_edma_device'
 static struct spi_board_info dm365_evm_spi_info[] __initconst = {
                              ^
arch/arm/mach-davinci/dm646x.c:603:42: note: 'dm646x_edma_device' was declared here
 static const struct platform_device_info dm646x_edma_device __initconst = {

This marks them const as well, as was originally intended.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>