arm: omap: map u_boot_lists section to .sram

Output section .u_boot_list was left unmapped in
u-boot-spl.lds for omap-common, causing the location
counter to roll back to bteween .rodata and .data,
making __image_copy_end and _end symbols wrong.

Mapping output section .u_boot_list to memory .sram
fixes these symbols' mapping.

This modifies the SPL binary but has no functional
impact, as __image_copy_end and _end are never used
in SPLs and u_boot_list is empty for all 29 boards
affected (omap4_sdp4430 eco5pk igep0030 am335x_evm_uart3
omap3_beagle am3517_crane igep0032 mt_ventoux pcm051
am3517_evm omap3_evm_quick_mmc am335x_evm_uart2
am335x_evm_spiboot am335x_evm_uart1 omap3_evm igep0030_nand
omap3_overo igep0020 am335x_evm omap4_panda omap5_evm
am335x_evm_uart4 devkit8000 tricorder mcx twister
omap3_evm_quick_nand am335x_evm_uart5 igep0020_nand).

Signed-off-by: Albert ARIBAUD <albert.u.boot@aribaud.net>