arm64: fix endianness annotation for 'struct jit_ctx' and friends

struct jit_ctx::image is used the store a pointer to the jitted
intructions, which are always little-endian. These instructions
are thus correctly converted from native order to little-endian
before being stored but the pointer 'image' is declared as for
native order values.

Fix this by declaring the field as __le32* instead of u32*.
Same for the pointer used in jit_fill_hole() to initialize
the image.

Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>