linux-user: Don't require PROT_READ for mincore

The kernel does not require PROT_READ for addresses passed to mincore.
For example the fincore(1) tool from util-linux uses PROT_NONE and
currently does not work under qemu-user.

Example (with fincore(1) from util-linux 2.38):

$ fincore /proc/self/exe
RES PAGES  SIZE FILE
24K     6 22.1K /proc/self/exe

$ qemu-x86_64 /usr/bin/fincore /proc/self/exe
fincore: failed to do mincore: /proc/self/exe: Cannot allocate memory

With this patch:

$ ./build/qemu-x86_64 /usr/bin/fincore /proc/self/exe
RES PAGES  SIZE FILE
24K     6 22.1K /proc/self/exe

Signed-off-by: Thomas Weißschuh <thomas@t-8ch.de>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20230422100314.1650-3-thomas@t-8ch.de>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>