arm64: fix endianness annotation for __apply_alternatives()/get_alt_insn()

get_alt_insn() is used to read and create ARM instructions, which
are always stored in memory in little-endian order. These values
are thus correctly converted to/from native order when processed
but the pointers used to hold the address of these instructions
are declared as for native order values.

Fix this by declaring the pointers as __le32* instead of u32* and
make the few appropriate needed changes like removing the unneeded
cast '(u32*)' in front of __ALT_PTR()'s definition.

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