Remove fudge factor from shoehorn

[kent-mcleod]

Correct the calculated memory needed to load an elf image. Using only
the p_memsz value ignores gaps between segments; instead calculate the
first+last addresses using p_vaddr & p_memsz.

As get_memory_usage in elf_sift.py now can calculate correct memory
usage from a list of ELF segments, a more accurate upper bound on
memory usage for the loaded apps is possible and the old fudge
factor is no longer needed.

Thanks to @sleffler for the patch.

[kent-mcleod]

There are some errors that I'll try and track down. The Elfloader is reporting that the loaded regions are all exclusive, however there appears to be consistent hanging before executing the kernel in some cases.

  ELF-loader started on CPU: ARM Ltd. Cortex-A53 r0p4
    paddr=[64b000..b5d117]
  No DTB passed in from boot loader.
  Looking for DTB in CPIO archive...found at 7c9528.
  Loaded DTB from 7c9528.
     paddr=[250000..254fff]
  ELF-loading image 'kernel' to 0
    paddr=[0..24ffff]
    vaddr=[ffffff8000000000..ffffff800024ffff]
    virt_entry=ffffff8000000000
  ELF-loading image 'sel4test-driver' to 255000
    paddr=[255000..64afff]
    vaddr=[400000..7f5fff]
    virt_entry=40e548
  Boot cpu id = 0x0, index=0
  
  [[Timeout]]
  None