riscv: dts: sifive unmatched: Fix regulator for board rev3

The existing values are rejected by the da9063 regulator driver, as they
are unachievable with the declared chip setup (non-merged vcore and bmem
are unable to provide the declared curent).

Fix voltages to match rev3 schematics, which also matches their boot-up
configuration within the chip's available precision.
Declare bcore1/bcore2 and bmem/bio as merged.
Set ldo09 and ldo10 as always-on as their consumers are not declared but
exist.
Drop ldo current limits as there is no current limit feature for these
regulators in the DA9063. Fixes warnings like:
  DA9063_LDO3: Operation of current configuration missing

Signed-off-by: Vincent Pelletier <plr.vincent@gmail.com>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>