[coreboot] [BUG] clear_memory triggers handle_deref_breakpoint()

[Petr Cvek]

Clearing the memory creates a situation, where an access to NULL pointer is actually valid. This causes a warning in the log:

clear_memory: Clearing DRAM 0000000000000000-0000000000005000
    Null dereference at eip: 0x7f3ca51d
    clear_memory: Clearing DRAM 000000000000a000-00000000000a0000

Should the test be disabled during clear_mem()?

Petr