omap: iovmm: don't check 'da' to set IOVMF_DA_FIXED flag

Currently IOVMM driver sets IOVMF_DA_FIXED/IOVMF_DA_ANON flags according
to input 'da' address when mapping memory:
da == 0: IOVMF_DA_ANON
da != 0: IOVMF_DA_FIXED

It prevents IOMMU to map first page with fixed 'da'. To avoid such
issue, IOVMM will not automatically set IOVMF_DA_FIXED. It should now
come from the user throught 'flags' parameter when mapping memory.
As IOVMF_DA_ANON and IOVMF_DA_FIXED are mutually exclusive, IOVMF_DA_ANON
can be removed. The driver will now check internally if IOVMF_DA_FIXED
is set or not.

Signed-off-by: David Cohen <dacohen@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>