testsuite: Adjust vect-bitfield-read-* with vect_shift and vect_long_long [PR107240]

The test cases vect-bitfield-read-* requires vector shift
target support, they need one explicit vect_shift effective
target requirement checking.  Besides, the vectype for struct
in test cases vect-bitfield-read-{2,4} is vector of long long,
we need to check effective target vect_long_long for them.
This patch can help to fix all remaining vect-bitfield-{read,
write}-* test failures on powerpc.

	PR testsuite/107240

gcc/testsuite/ChangeLog:

	* gcc.dg/vect/vect-bitfield-read-1.c: Add effective target checking
	vect_shift.
	* gcc.dg/vect/vect-bitfield-read-3.c: Likewise.
	* gcc.dg/vect/vect-bitfield-read-5.c: Likewise.
	* gcc.dg/vect/vect-bitfield-read-6.c: Likewise.
	* gcc.dg/vect/vect-bitfield-read-7.c: Likewise.
	* gcc.dg/vect/vect-bitfield-read-2.c: Add effective target checking
	vect_shift and replace vect_int with vect_long_long.
	* gcc.dg/vect/vect-bitfield-read-4.c: Likewise.