Fix unaligned load with small memcpy on the ARM

Fix unaligned load with small memcpy on the ARM

store_integral_bit_field is ready to handle BLKmode fields, there is
even a subtlety with their handling on big-endian targets, see e.g.
PR middle-end/50325, but not if they are unaligned, so the fix is
simply to call extract_bit_field for them in order to generate an
unaligned load.  As a bonus, this subsumes  the big-endian specific
path that was added under PR middle-end/50325.

	PR middle-end/92071
	* expmed.c (store_integral_bit_field): For fields larger than a
	word, call extract_bit_field on the value if the mode is BLKmode.
	Remove specific path for big-endian targets and tidy things up a
	little bit.