ARM: omap: fix address space warnings from sparse

Moving sram code from plat-omap got the attention of the kernel test robot.

I found a few more places with related warnings because the sram
references are a mix of kernel pointers and __iomem pointers:

mach-omap1/sram-init.c:56:17: warning: cast removes address space '__iomem' of expression
mach-omap1/board-ams-delta.c:667:9: warning: incorrect type in argument 1 (different base types)
mach-omap2/sram.c:78:17: warning: cast removes address space '__iomem' of expression
mach-omap2/omap4-common.c:142:27: warning: incorrect type in assignment (different address spaces)
mach-omap2/omap4-common.c:142:27:    expected void [noderef] __iomem *static [toplevel] sram_sync
mach-omap2/omap4-common.c:142:27:    got void *
mach-omap2/pm34xx.c:113:45: warning: incorrect type in argument 1 (different address spaces)
mach-omap2/pm34xx.c:113:45:    expected void [noderef] __iomem *save_regs
mach-omap2/pm34xx.c:113:45:    got void *extern [addressable] [toplevel] omap3_secure_ram_storage

There is no good solution here, as sram is a bit special in this
regard. Change the annotations to at least shut up the warnings.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>