mtd: hyperbus: move direct mapping setup to AM654 HBMC driver

The Hyperbus core expects that HyperFlash is always directly mapped for
both read and write, but in reality this may not always be the case, e.g.
Renesas RPC-IF has read only direct mapping. Move the code setting up the
direct mapping from the Hyperbus core to thh TI AM554 HBMC driver.

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>