exec: add endian specific phys ld/st functions

exec: add endian specific phys ld/st functions

Device code some times needs to access physical memory and does that
through the ld./st._phys functions. However, these are the exact same
functions that the CPU uses to access memory, which means they will
be endianness swapped depending on the target CPU.

However, devices don't know about the CPU's endianness, but instead
access memory directly using their own interface to the memory bus,
so they need some way to read data with their native endianness.

This patch adds _le and _be functions to ld./st._phys.

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>