hw/core/loader: Let load_elf() populate a field with CPU-specific flags

hw/core/loader: Let load_elf() populate a field with CPU-specific flags

While loading the executable, some platforms (like AVR) need to
detect CPU type that executable is built for - and, with this patch,
this is enabled by reading the field 'e_flags' of the ELF header of
the executable in question. The change expands functionality of
the following functions:

  - load_elf()
  - load_elf_as()
  - load_elf_ram()
  - load_elf_ram_sym()

The argument added to these functions is called 'pflags' and is of
type 'uint32_t*' (that matches 'pointer to 'elf_word'', 'elf_word'
being the type of the field 'e_flags', in both 32-bit and 64-bit
variants of ELF header). Callers are allowed to pass NULL as that
argument, and in such case no lookup to the field 'e_flags' will
happen, and no information will be returned, of course.

CC: Richard Henderson <rth@twiddle.net>
CC: Peter Maydell <peter.maydell@linaro.org>
CC: Edgar E. Iglesias <edgar.iglesias@gmail.com>
CC: Michael Walle <michael@walle.cc>
CC: Thomas Huth <huth@tuxfamily.org>
CC: Laurent Vivier <laurent@vivier.eu>
CC: Philippe Mathieu-Daudé <f4bug@amsat.org>
CC: Aleksandar Rikalo <aleksandar.rikalo@rt-rk.com>
CC: Aurelien Jarno <aurelien@aurel32.net>
CC: Jia Liu <proljc@gmail.com>
CC: David Gibson <david@gibson.dropbear.id.au>
CC: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
CC: BALATON Zoltan <balaton@eik.bme.hu>
CC: Christian Borntraeger <borntraeger@de.ibm.com>
CC: Thomas Huth <thuth@redhat.com>
CC: Artyom Tarasenko <atar4qemu@gmail.com>
CC: Fabien Chouteau <chouteau@adacore.com>
CC: KONRAD Frederic <frederic.konrad@adacore.com>
CC: Max Filippov <jcmvbkbc@gmail.com>
Reviewed-by: Aleksandar Rikalo <aleksandar.rikalo@rt-rk.com>
Signed-off-by: Michael Rolnik <mrolnik@gmail.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Aleksandar Markovic <amarkovic@wavecomp.com>
Message-Id: <1580079311-20447-24-git-send-email-aleksandar.markovic@rt-rk.com>