kexec_load.2: Incorporate fixes from Eric W. Biederman

kexec_load.2: Incorporate fixes from Eric W. Biederman

Eric noted that a few instances of "virtual" should
be "physical" and noted:

    There is an expectation that at hand off from sys_kexec that
    virtual and physical addresses will be identity mapped. But
    this isn't the old Alpha booting convention where you have
    a virtual address and then you have to parse the page table
    to figure out where your kernel was actually loaded.

Reported-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>