S390: Use 64bit instruction to check for copies of > 1MB with mvcle.

S390: Use 64bit instruction to check for copies of > 1MB with mvcle.

The __memcpy_default variant on s390 64bit calculates the number of
256byte blocks in a 64bit register and checks, if they exceed 1MB
to jump to mvcle. Otherwise a mvc-loop is used. The compare-instruction
only checks a 32bit value.
This patch uses a 64bit compare.

ChangeLog:

	* sysdeps/s390/s390-64/memcpy.S (memcpy):
	Use cghi instead of chi to compare 64bit value.