[ARM] 4102/1: Allow for PHYS_OFFSET on any valid 2MiB address

This patchs allows the offset to the first page of
physical memory to be on any 2MB boundary
whereas the previous code could only handle psysical
offset to any 16MB boundary (0xNN000000) or any 1MB
boundary below 0x01000000 (e.g. 0x00N00000). The
problem is a consequence of the orr one-byte syntax,
so we fix this and we can place the first bank of
memory at 0x28e00000. I have also included an explicit
check that disallow compilation when PHYS_OFFSET is
not on a 2MiB boundary. head.S would be the proper place
to have this at since this is the first file that
attempts to use PHYS_OFFSET during compile.

Signed-off-by: Linus Walleij <triad@df.lth.se>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>