usb: ehci: Fix accessors for big-endian platforms and descriptors

Commit 9000eddb ("drivers/usb/ehci: Use platform-specific accessors")
broke USB 2.0 on big-endian platforms because for them writel/readl()
does automatic conversion of BE data to LE.

Proper implementation requires to use "raw" variant of these accessors
which read/write data without messing with endianess.

While at it replace cpu_to_be32() to be32_to_cpu() in readl() to
keep sane semantics.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Marek Vasut <marex@denx.de>
Reported-by: Vladimir Boroda <boroda@yahoo.com>