[sh4] memory mapped TLB entries

SH4 MMU's memory mapped TLB feature is implemented.
SH-Linux seems to write to memory mapped TLB to invalidate a TLB entry,
but does not to read it. So only memory write feature is implemented.
Work on memory read feature is left.

(Shin-ichiro KAWASAKI)

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5067 c046a42c-6fe2-441c-8c8c-71466251a162
