Compile loader only once

Compile loader only once

Callers must pass ELF machine, byte swapping and symbol LSB clearing
information to ELF loader. A.out loader needs page size information, pass
that too as a parameter.

Extract prototypes to a separate file. Move loader.[ch] and elf_ops.h under hw.

Adjust callers. Also use target_phys_addr_t instead of target_ulong for
addresses: loader addresses aren't virtual.

Signed-off-by: Blue Swirl <blauwirbel@gmail.com>