arm/km: introduce bootcount env variable and clean km_arm

arm/km: introduce bootcount env variable and clean km_arm

This environment variable is used to set the bootcount address
for the kernel.

last_stage_init is not available for arm platforms. So the
calls to set_km_var and set_bootcount_addr are done in
misc_init_r.

Additionally some unneeded printouts were removed.

Signed-off-by: Valentin Longchamp <[email protected]>
Signed-off-by: Holger Brunck <[email protected]>
Acked-by: Heiko Schocher <[email protected]>
cc: Wolfgang Denk <[email protected]>
cc: Detlev Zundel <[email protected]>
cc: Prafulla Wadaskar <[email protected]>