or1k: Add return address argument to _mcount call

This fixes an issue in the glibc port I am working on where the build
fails due to the warning:

  error: calling ‘__builtin_return_address’ with a nonzero argument is unsafe [-Werror=frame-address]

This is due to how the current implementation of _mcount in glibc uses
__builtin_return_address with a count argument of 1.

Fix that by passing the value of LR_REGNUM to the _mcount function,
effectivtly providing the value _mcount is after.

This is an ABI change, but I think it's OK because the glibc port for
or1k is not yet upstreamed.  Also, I think just adding an argument
should not break anything anyway.

gcc/ChangeLog:

	* config/or1k/or1k.h (PROFILE_HOOK): Add return address argument
	to _mcount.