broadcom-wl: Fix compilation with kernel 5.10

broadcom-wl: Fix compilation with kernel 5.10

This adds a few fixes for compiling against Linux 5.10:

1. segment_eq() has been removed with upstream commit
   428e2976a5bf7e7f5554286d7a5a33b8147b106a ("uaccess: remove
   segment_eq") and can use uaccess_kernel() instead
2. ioremap_nocache() is removed and is now an alias for ioremap() with
   upstream commit 4bdc0d676a643140bdf17dbf7eafedee3d496a3c ("remove
   ioremap_nocache and devm_ioremap_nocache")

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
(cherry picked from commit cd3de51bb4a18f922a961fdeb42c1c8f1f80b425)