rinato: Expose ATAGS cmdline to userspace

[casept]

Needed to figure out device identifiers and boot mode (normal, recovery, charging only)

[casept]

Just enabling ATAGS and ATAGS_PROC seems insufficient (kernel prints No ATAGs?).

The atags saved by the kernel just looks like an all-zero region.

But it doesn't seem to pass it via DTB either (even though it detects that we're booting a DT-enabled kernel).

The cursed way to go about this would be to pull it out of the S-Boot logs in memory (strings of the form ATAG_CMDLINE: 76 54410009 'console=ram loglevel=4 root=/dev/mmcblk0p15 ro rootfstype=ext4 rootwait bootmode=normal pwron.reason=ap:swrst,pmic:pwron sec_debug.enable=1 sec_debug.enable_user=1 softlockup_panic=0 sec_log=0x200000@0x46000000 lcdtype=0 oops=panic pmic_info=1875 sysscope=0xee000000 cordon=ed54f2b82322ef31ecc35db3b049264c serialno=4100cd38423931e5 tizenboot.emmc_checksum=3 tizenboot.odin=1 bootloader.ver=R380XXU0BOA2 bootloader.fb=0x48000000 bootloader.log=0x15d2@0x4600485d'), but that'd require logic to figure out which of the entries in there pertains to the current boot.