OMAP3: EVM: Convert omap3_evm_version to u32

Convert the variable omap3_evm_version to u32 to work around
some broken linkers from older tool chains. E.g. CodeSourcery's
2009q1-203 ld 2.19.51.20090205. Without this, these linkers
stop linking 'omap3_evm' or at least issue a warning. Like

arm-none-linux-gnueabi-ld: section .bss [8003f5e0 -> 8007e337] overlaps section .rel.dyn [8003f5e0 -> 80044e57]
arm-none-linux-gnueabi-ld: section .dynsym [80044e58 -> 80044ef7] overlaps section.bss [8003f5e0 -> 8007e337]
arm-none-linux-gnueabi-ld: u-boot: section .bss vma 0x8003f5e0 overlaps previous sections

CC: Sanjeev Premi <premi@ti.com>
Signed-off-by: Dirk Behme <dirk.behme@googlemail.com>