testsuite: aarch64: Fix failing SVE tests on big endian

testsuite: aarch64: Fix failing SVE tests on big endian

A recent change "gcc: Add vec_select -> subreg RTL simplification"
updated the expected test results for SVE extraction tests. The new
result should only have been changed for little endian. This patch
restores the old expected result for big endian.

gcc/testsuite/ChangeLog:

2021-07-15  Jonathan Wright  <jonathan.wright@arm.com>

	* gcc.target/aarch64/sve/extract_1.c: Split expected results
	by big/little endian targets, restoring the old expected
	result for big endian.
	* gcc.target/aarch64/sve/extract_2.c: Likewise.
	* gcc.target/aarch64/sve/extract_3.c: Likewise.
	* gcc.target/aarch64/sve/extract_4.c: Likewise.