This makes life easier when calling e.g. `saul_reg_write()` with data
stored in flash.
As now the signatures for reading and writing differ (in that `const`
qualifier only), `saul_notsup()` is split into `saul_write_notsup()`
and `saul_read_notsup()`. However, one is implemented as a symbol alias
of the other, so that ROM consumption remains unchanged.
This changes the prefixes of the symbols generated from USEMODULE and
USEPKG variables. The changes are as follow:
KCONFIG_MODULE_ => KCONFIG_USEMODULE_
KCONFIG_PKG_ => KCONFIG_USEPKG_
MODULE_ => USEMODULE_
PKG_ => USEPKG_
First, every read function converts the void pointer into a const bmx055_t
Second, it is cleaner (more obvious) to pass phydat_t.val[3] instead of
type casting to int16_t* and relying that .val[3] is the first struct
member of phydat_t.
