hw/core/loader.c: Improve reporting of ROM overlap errors

hw/core/loader.c: Improve reporting of ROM overlap errors

In rom_check_and_register_reset() we report to the user if there is
a "ROM region overlap". This has a couple of problems:
 * the reported information is not very easy to intepret
 * the function just prints the overlap to stderr (and relies on
   its single callsite in vl.c to do an error_report() and exit)
 * only the first overlap encountered is diagnosed

Make this function use error_report() and error_printf() and
report a more user-friendly report with all the overlaps
diagnosed.

Sample old output:

rom: requested regions overlap (rom dtb. free=0x0000000000008000, addr=0x0000000000000000)
qemu-system-aarch64: rom check and register reset failed

Sample new output:

qemu-system-aarch64: Some ROM regions are overlapping
These ROM regions might have been loaded by direct user request or by default.
They could be BIOS/firmware images, a guest kernel, initrd or some other file loaded into guest memory.
Check whether you intended to load all this guest code, and whether it has been built to load to the correct addresses.

The following two regions overlap (in the cpu-memory-0 address space):
  phdr #0: /home/petmay01/linaro/qemu-misc-tests/ldmia-fault.axf (addresses 0x0000000000000000 - 0x0000000000008000)
  dtb (addresses 0x0000000000000000 - 0x0000000000100000)

The following two regions overlap (in the cpu-memory-0 address space):
  phdr #1: /home/petmay01/linaro/qemu-misc-tests/bad-psci-call.axf (addresses 0x0000000040000000 - 0x0000000040000010)
  phdr #0: /home/petmay01/linaro/qemu-misc-tests/bp-test.elf (addresses 0x0000000040000000 - 0x0000000040000020)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20201129203923.10622-3-peter.maydell@linaro.org