abitypes.h: Remove incorrect ARM ABI_LLONG_ALIGNMENT

abitypes.h: Remove incorrect ARM ABI_LLONG_ALIGNMENT

The ARM EABI specifies that 64 bit integers should be
8 aligned; remove our incorrect setting of 4 alignment.
This has no actual effect since it only set the alignment
for the 'abi_ullong' and 'abi_llong' types, which are used
only inside code which is MIPS-specific, but it will
avoid problems later if we use the types elsewhere.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>